their productive powers, that one chaldron of coal would yield twenty-five thousand cubic feet of gas, and two chaldron of coke.*

The purity of coal gas is a circumstance of so much importance, that it has given rise to a great variety of contrivances for the purpose of effecting its purification. In the greater number of inventions, the object has been the effective application of lime, either in a dry state, or mixed with water to the consistence of cream; but the vessels for this operation have greatly varied, either in form or construction. As early as 1811, Mr. Clegg had introduced a separate machine for purifying coal gas, but that which is included in his patent he called the Semi-fluid Lime Machine, from its object being to purify the gas by means of Cream of lime. The outside case of this machine was constructed in the form of a large hopper, the upper part of which was an oblong square, and in this part the trough was fixed that contained the semi-fluid mixture. A strong shaft

* This is stated in a pamphlet which Mr. Clegg published in 1820.

+ Dr. Henry mentioned, in 1805, the washing of coal gas with lime-water as the means of purifying it from sulphuretted hydrogen; afterwards, in 1808, he stated that the mixture of lime and water (cream of lime) would completely effect it; and Mr. Clegg's were the first mechanical contrivances to carry Dr. Henry's views into practice.

or spindle passed horizontally through its whole length, and to this shaft a number of arms or paddles were attached, so that, by means of the motion given by a winch, the mixture could be con stantly agitated while the gas was passing through it. When the mixture was saturated, and required to be changed, the vessel had a contrivance by which it was inverted, and its contents fell into the hopper beneath, to pass away through a large pipe affixed to the bottom of it, and conveyed into a vault below, whence it might be readily removed. This was obviously a great improvement upon all the methods which had previously been employed for the purification of coal gas; for, by keeping the semi-fluid mixture continually in motion, every part of it was exposed that it might come into contact with the gas, and by its chemical action deprive it of those noxious substances and impurities that were mixed with it, and had a tendency to be productive of inconvenience by their odours, or, if inhaled, might be injurious to health.

Another part of Mr. Clegg's patent was the Gas Meter; and although this machine was neither so simple in its first construction, nor so correct in its operations, as it has since been rendered by subsequent improvements, it must be allowed to have been a most useful invention. He had previously devised and constructed a Gasholder, in the form of that portion of a circle which makes

two hundred and fifty degrees, and which moved vertically upon a horizontal axis, and acted upon the principle of the hydraulic bellows. As the circle was accurately graduated, to indicate the quantity of gas entering in, or passing out, of the machine, probably it was this circumstance that suggested to Mr. Clegg the original idea of his Gas Meter. This was certainly a most ingenious contrivance; and though its principle may be easily understood, perhaps the machine was rather too complicated to be rendered intelligible by mere verbal description. The part forming the interior consisted of a hollow wheel or drum, which was accurately divided into several compartments; the wheel moved upon a hollow axis, and was inclosed in an air-tight case, which was a little larger than itself. Both the outer case and the lower chambers of the wheel were filled with water rather higher than the axis; and each compartment had two apertures, one for admitting the gas to enter in, and the other for its passage out. When the gas was entering into any one compartment, its outlet orifice was below the surface of the water, while the adjoining chamber had its outlet aperture above the water, and of course was discharging the gas to pass to the burners. Thus, by the combined effect of the alternate and successive filling and emptying of the respective compartments, the wheel was made to revolve. As its

axis was connected with, and communicated motion to, a series of wheel-work, which registered its revolutions, the exact quantity of gas that passed through the meter was ascertained; and the number of cubic feet was shewn by an index and dial-plate. When Mr. Clegg obtained his patent he had introduced some scrolls and stuffing-boxes into its arrangement, which rather impeded the facility of its action, and rendered it liable to obstructions; but these have since been obviated. Whatever may have been the defects of its first form and construction, it is perhaps the most original and beneficial of all the various inventions of which Gas-lighting has been the occasion. Its utility must be strikingly evident, and the correctness of its operations excite admiration.*

* Though the original invention and construction of the Gas Meter is unquestionably due to Mr. Clegg, it has been very materially improved by Mr. Samuel Crosley, the present proprietor of the patent. The experience of several years has proved its advantages, both to the proprietors of gasworks, and the consumers of gas; and its utility has been evinced by the regularity and accuracy of the operations by which its purposes are effected. Though so extensively employed, it is rather surprising that so useful an instrument should not have become more generally introduced; but some great companies even now object to its use by their customers, though its obvious tendency appears to be in di

When both the novelty and the magnitude of the establishments which have originated in Gaslighting are considered, it must be obvious that they afforded a powerful stimulus for the exhibition of talent and the exercise of ingenuity. By their united efforts they have extended the boundaries of art, and enriched it with inventions; and several of these have not only conduced to accelerate the progress of the new mode of lighting, but have also proved peculiarly beneficial to its interests. Although the average quantities of gas which could be obtained from different kinds of coal had been deduced from the results of a variety of experiments, it was essential to the welfare of such concerns as those for the production of gas upon an extensive scale, that the means should be devised to ascertain with readiness and accuracy

rect unison with their interests. For as they may fix their own price, and all the gas consumed is registered by the Meter, the company have the satisfaction to know that every cubic foot of gas that passes through it must be paid for; besides, by its enabling the consumer to burn any number of lights, and in any way that his taste or occasions may require, it is a satisfaction for him to know that he is paying for the quantity he alone uses, and not for the waste of his neighbours. From a variety of considerations, it seems probable that Gas-lighting would become more general than it is at present, were the employment of Meters more universally adopted.