Immediately below it, within the box, is a white screen capable of adjustment at different angles and two small electric lamps of different candle-power, either or both of which can be used. A portable secondary battery is used to supply them with current. The illumination of the hinged screen inside the box varies approximately as the cosine of the angle of incidence of the light from the electric lamps upon it. A handle with a pointer moving over a graduated scale is connected to the screen with a system of levers, and the inclination is so adjusted that the illumination of the screen is equal to that of the perforated diaphragm, the perforations seeming to disappear when this balance is affected. The illumination can then be read off on the scale in units of the illumination due to one standard candle at one foot distance. The object of the levers is to give an open and convenient scale. The scale is graduated by experiment, and does not depend upon the cosine law. The colour difficulty, where arc light or daylight is to be measured, is reduced by the use of & yellow-tinted diaphragm and a blue-tinted screen, the tints being selected so that the readings are the same as the mean of a large number of measurements made with white screens. By means of a graduated quadrant and a gnomon the angle and the cosine of the angle of incidence of the light from a lamp may be measured, and rules are given for deducing the height of the lamp and the slant height, and hence the candle-power of the lamp.

3. On Storage Batteries. By H. A. EARLE.

The author traced the history of storage batteries from the time when Gautherot, in 1801, obtained secondary currents from silver and platinum plates which had been used in a voltameter to decompose a saline solution. Ritter, in 1803, was the first to make a secondary battery, in which he employed plates of gold separated by cloth or paper, moistened with a saline solution; and though he employed various metals, including lead, the secondary currents he obtained were only of short duration, and the batteries of only scientific interest. It would naturally be presumed that he would have noticed increased effects when using lead, but we find that he used salt water and not an acid solution, and on this account chloride of lead was formed, which is scarcely soluble and is a bad conductor.

De la Rive in 1826 obtained secondary currents from platinum plates in a voltameter filled with water, and he closely approached the elements of our present storage cells when, among his many experiments, he used in a primary battery a platinum plate covered with a film of peroxide of lead, and a zinc plate immersed in an acid solution.

The first powerful storage battery was introduced by Planté in 1860, but the method employed for its formation was too long and costly for practical purposes. Faure, in 1881, reduced this long process of formation by applying lead oxide in the form of a paste to the surfaces of the plates, but the adhesion was insufficient, and the life of the cells was too short to give them commercial value. Swan realised that the active material required a better mechanical support, and introduced a plate of grid form, the interstices serving to retain the material; and this frame, combined with the Faure pasting, was the origin of the plates largely used in this country and elsewhere.

The monopoly that existed for the manufacture of this plate caused other makers to turn their thoughts to the plain lead plates, and such great advances have been made both in their manufacture and method of formation, that it is rapidly replacing the pasted form.

A type that differs greatly from the solid lead plate, but which is not pasted, is the chloride plate, in which the material to become active is a mixture of chloride of lead and chloride of zinc cast into small tablets, which are framed by casting antimonious lead around them under high pressure. The subsequent elimination of the chloride and zinc leaves a porous structure of pure lead of a crystalline nature, of good conductivity, and with a large surface exposed to the electrolyte, the result being a large capacity for a given weight, and for the space occupied.

Omitting the question of cost, the chief points to be considered in connection with accumulators are-the chemical action, the mechanical construction, and the proper treatment of the cells when made.

The theoretical value of lead peroxide is 4:44 grammes per ampere hour, or, roughly, one pound is the equivalent of 100 ampere hours. Presuming that the positive and negative plates were identical, the value would be approximately 50 ampere hours for one pound of peroxide and spongy lead. As a matter of fact, the highest capacity plates yield only about seven ampere hours per pound of positive and negative plates, or sixteen ampere hours per pound of peroxide and spongy lead, due to the facts that a conducting frame of considerable weight has to be employed, and to the impossibility in practical working of reducing the whole of the peroxide. To obtain the best results for a given weight the frame must be reduced to a minimum consistent with the necessary strength and conductivity, and the distribution of the peroxide must be such as to admit of the perfect circulation of the electrolyte, and its penetration throughout the mass.

The behaviour of cells under various conditions is most interesting, and from the curves that can be plotted we can readily study the effects due to different rates of charge and discharge, to the penetration and strength of the electrolyte, and to the ratio of the weights of the positive and negative plates.

There is a given rate of charge which is most suitable to each type of cell, mainly due to the disposition of the active material, to its thickness, and to the method of its production, namely, whether it has been mechanically applied or electrolytically produced. Most of the effects of varying rates of charge can be ascertained from the resultant discharges, but discharge curves have nevertheless characteristics of their own, which are to a great extent unconnected with the conditions of charges.

A series of curves was exhibited to the Section which gave the capacities of seven types of plates at present in use; the yield was given in ampere hours per pound of positive and negative plates, the weight of one positive and one negative being taken in each instance; the variation in capacity for high and low rates of discharge was also shown.

The striking point in these curves is the great variation existing in the various types of plates now in use, but this can be explained, to a great extent, for the heavy solid plates, the active material of which is formed out of the plates themselves, must have a large reserve of weight to give them life, while pasted plates, or plates with a large area, fall higher on the curve. the others in capacity, and this is due to the nature of the active material, which One plate greatly exceeds all permits the penetration of the electrolyte throughout the mass.

Regarding the voltage of a discharging cell, this varies greatly, and is dependent upon the rate of discharge, the strength of the electrolyte, and other causes. In considering this question, it will not be out of place to draw attention to conditions frequently met with in specifications for storage batteries.

In some instances a given percentage in fall of voltage is allowed; in others the voltage per cell is fixed to a hundredth of a volt, above which limit it must give the specified capacity. This type of specification is, as a rule, most unsatisfactory, for at what point does our initial voltage start? On open circuit? Immediately on closing the circuit, or five minutes afterwards? Further, may the cells stand for half a day after charging before the discharge is taken? The best way to meet this latter case is to take the first reading of voltage after the cell has commenced discharging, and when 3 per cent. of the specified discharge period has elapsed.

The most satisfactory specification to all concerned is for the amperes to be specified, and the time for which the discharge is to be maintained, the voltage of the complete battery at the end of the discharge being also given, the number of cells being omitted; this would require for a low voltage discharge per cell an increased number of cells, but a decreased number of plates, or vice versá; and the author finds that this would not admit of the individual cells being worked to too low a voltage, and that the purchaser would obtain exactly what he requires at the lowest price.

When tests are made to check the efficiency and capacity of a battery, we can place no reliance on the figures obtained from a single charge and discharge; as a rule no two consecutive discharges are identical, even when discharged with the same current and down to the same voltage. In tables given in the paper the first ten charges and discharges from a new cell are recorded. These give a good idea of the very various nature of results obtainable with slight differences of charge. The figures show that the higher the voltage to which the cell is raised on charge, the lower the efficiency, and also that a change of condition of charge may increase or decrease the efficiency and output to an extraordinary extent.

The strength of the acid solution used has a great effect upon the behaviour of a cell, also upon its life and voltage; moreover, a weak solution has a high resistance, which diminishes as acid is added, till a specific gravity of about 1-250 is reached, when any addition of acid rapidly increases the resistance; the resistance also rapidly increases as the temperature falls. Each type of cell works best with a given strength of acid, but there are other most important points to be considered, namely, that different strengths of the electrolyte have great effect both on the capacity of the cell and upon its voltage.

Acid solutions of specific gravity from 11 to 13 will vary the voltage as much as 10 per cent., and the highest capacities for various types of plates are obtained with acid from specific gravity 12 to 13, and beyond these limits only a small percentage of the maximum capacity can be obtained, and the curves of mean voltage for different strengths of acid bear a most interesting relation to the various curves of capacity under the same conditions.

The action upon plates when first erected and immersed in the electrolyte can, to a great extent, be investigated by the fali and rise of its specific gravity, various results being obtained from plates in different states, and according to whether they are left standing or immediately charged. The conclusions drawn from many tests of this nature is, that fully formed positives with clean negatives are but little affected by standing, while partially formed positives and oxidised negatives sulphate rapidly.

Regarding the treatment of cells and their life the chief causes of destruction are impure acid solution, too prolonged or excessive rates of discharge, insufficient charging, overcharging, long periods of rest on open circuit without charging, and allowing cells to remain after complete discharge for many hours before recharging.

We find, therefore, that many causes influence the working and life of storage batteries, and that many of these can be varied at will; the problem, therefore, is to so combine all useful effects, that the best possible article is produced with due consideration to cost.

In a secondary battery we have lead, sulphuric acid solution, and the resultant compounds, and nothing else. The ideal cell is one that is indestructible, and this being given, the first cost and weight, if kept within reasonable limits, are of little moment.

At the present moment the life of a cell is its value, and its death is brought about by the disintegration of the active material. Now this disintegration is what we have to stop, the material is as good as ever, for nothing is wasted, and provided it were held in perpetual, firm, and good electrical contact with the frame in such a manner that the free circulation and penetration of the acid were not hindered, and the internal resistance not unduly increased, we should have produced an ideal and indestructible cell.

The author has discussed only a few of the many interesting features in connection with secondary batteries, being results obtained in practice.

4. The Development of the Telephone Service in Agricultural Districts. By Major-General WEBBER, C.B., R.E., M.Inst.C.E.

On April 20, 1895, the 'Times' published a letter from the author on the subject in which public attention was drawn to the probability that the telephone, as well as light railways, might be beneficial to rural districts.

On May 14, 1895, in examination before the parliamentary committee which inquired into the development of the telephone service in the United Kingdom, the author also gave evidence on this subject.

He brings the subject before this Section in hopes that it may elicit discussion by practical telephone engineers. It need hardly be said that his selection of the county of Suffolk as an example of what can be done is especially appropriate to this meeting of the Association.

The map shown to illustrate the paper was the Ordnance survey, on a scale of 1 inch to 1 mile. Every town, village, or hamlet where a post office is situated is marked with a blue disc, and at each of these a telephone call-office would be established. When this is also a telegraph office a red flag is added, and at the twenty-nine towns where it is proposed that telephone exchanges should be established the blue disc is surrounded by a ring in red.

The total number of call-offices is 29.

The lines of railway on which there are postal telegraph wires are shown in red, those on the roads in blue, and the proposed extensions for telephones to the proposed call-offices in green.

Probable connections to private subscribers are not shown. These will be, in most cases, by means of twin wires on the same poles. In the case of all the 351 call-offices the communication will be by single conductors and earth-returns, the connections between the exchanges themselves being by twin wires.

It is thought probable that, whether the Post Office erects such a system in the country or not, there will be no difficulty in using the spare space on the existing Post Office poles, for which, if the work is not undertaken by the Post Office, a way leave to that department would be earned for the public

revenue.

In most cases the railways have been avoided owing to the excessive charges for way leave and maintenance.

It is not proposed that these lines should be constructed with so costly material as that used by the Post Office.

If carried out by the County Council the whole of the work could be tendered for, and the poles supplied locally, and very little special labour would be required.

The poles, insulators, brackets, and wire will be of the same size as is used everywhere for light, permanent, military telegraph lines, and quite as efficient and lasting as the heavier material. The conditions are: 25 poles to the mile; small single shed porcelain insulators; screw brackets having a bent shank; the conductors to be of No. 16 bronze, and to be stretched within 9 inches vertically of one another.

The exchange offices will be placed either in county buildings or in private houses; the call-offices in private houses, where a small payment of 97. per annum, with a percentage on the receipts above an average of 28. a day gross, will suffice for rent, and for attendance, which could be given by a child over ten or twelve.

A revenue from the subscriptions of private subscribers may be anticipated, the subscriptions to vary between 67. and 107. a year, according to circumstances, situation, and services given.

The official use of the system by the county authorities is a value which the chief constables, surveyors, and clerks to the councils could probably estimate better than the author can.

The being able to converse with salesmen, markets, other farms, outlying bailiffs, and workmen is an assistance to agriculture which is apparently obvious. Small tradesmen will be able by it to keep trade in local hands. Regulations of transport and carriage of all kinds will be assisted.

Economies will be effected in distribution of perishable agricultural produce of all kinds.

Farm labour, male and female, would have improved means of obtaining information as to demand and supply.

The proposed charge for a 'talk' would be 2d. within one exchange area, 3d. beyond and inside the county.

How far this would affect the Post Office revenue in its various branchestelegraph, postal, and parcels-it is not easy to estimate. The author believes that compensation for losses in one direction will always be found in another.

5. Some Lessons in Telephony. By A. R. BENNETT, M.Inst.E.E.

It has recently been demonstrated that the development of telephonic communication in the United Kingdom is inferior to that which has been attained in many foreign countries.

Why this is so may best be discovered by ascertaining by what means, technical or economical, those nations which have most conspicuously outstripped us have acquired their superiority. For the purposes of this paper the countries of Europe have been divided into three groups: (1) well telephoned; (2) indifferently telephoned; (3) badly telephoned.

A country may most properly be said to be well telephoned when its smaller towns and villages enjoy facilities; for the existence of a few large exchanges in the capital and chief towns does not entitle it to that distinction. France, Russia and Portugal all possess good exchanges in their capitals, but are nevertheless badly telephoned, since their smaller towns and villages are excluded from participating in the service. On the other hand we find that Norway, Sweden, Switzerland, Luxemburg, Denmark and Finland are in the first rank as well-telephoned countries, since not only their capitals and chief towns, but their villages and even hamlets, are provided with communication. With them the telephone is no longer a luxury, but an adjunct of everyday life, within reach of even the poorest.

Of these six countries, which compose Group I., four owe their development to companies and co-operative societies, and two-Switzerland and Luxemburgto their Governments.

A considerable gap exists between the worst country of Group I. and the best of Group II. This is the German Empire, exclusive of Bavaria and Würtemberg, which possess their own systems independently. Thereafter the countries follow in the order indicated in the Table, which shows that Norway is the best and Russia the worst telephoned country of Europe.

The questions naturally arise, 'To what causes are such vast differences in development to be ascribed?' and 'Why is the United Kingdom, with its preponderating commercial importance and unparalleled spirit of enterprise, only tenth on the list, instead of first ?'

A study of the table supplies the answer. It shows that telephonic development is proportional to the prevalence of the following features:

(1) Low rates; (2) Local management of exchanges; (3) Facilities for rural intercourse; (4) Competition.

At least three of these are characteristic of each of the six countries which compose Group I.

On the other hand, they are almost completely absent from Groups II. and III., the leading characteristics of which are:

(1) High rates; (2) Centralised management; (3) Neglect of small towns and rural districts; (4) Absence of competition.

On inquiring in what manner circumstances differ so greatly in the United Kingdom as to preclude the possibility of small towns and rural communities sharing in telephonic communication, it appears that the inelasticity of the prevalent system of tariffs, which was originally invented for towns, is chiefly to blame. In towns distances are short, and subscribers, if the switch-rooms are properly distributed, have seldom to pay more than the unit charge; but in country districts distances of several miles must often intervene between the subscriber and switch-room, and as the annual rental exacted increases rapidly with the distance, the charges become piled up by the extra mileage entirely beyond the means of the vast majority of the people. What is wanted is the application of the Austrian (which, with some modifications, has also been adopted in Luxemburg) system of tariffs, and under which all subscribers, whatever their distance