by hour lines, in order to indicate the time. The paper thus prepared is folded round, and attached to, a cylinder, which is connected with, and moved by, a time-piece; hence, the line described by the pencil shews at once the degree of pressure, and denotes the time.

The following table exhibits the form of the paper with its various horizontal and vertical divisions, on which both the pressure and time are inscribed by the black-lead pencil, as the cylinder moves the paper.

Mr. Crosley has recently contrived a simple but an ingenious instrument for indicating and registering the impurities of the gas, and which, at the same time, denotes the periods when they Occur.*

The arrangement of this apparatus consists of a circular card placed upon an axis, which communicates with a time-piece. Upon this card three

* Would not Katascope be an appropriate term for this instrument, from the Greek word 'Katascopos,' an explorer or observer?

circles are described which are divided into 24 divisions by lines drawn from the centre, corresponding with the hours of day and night. The two largest circles, (A, B,) which are of equal breadth, occupy the marginal space at the outer extremity of the card; these are coated with the usual solutions or tests for sulphuretted hydrogen and ammonia, and a very small jet of gas, from an orifice adapted to each of the circles, is made to play constantly over them. The inner circle being divided into spaces that are marked from 1 to 12 for DAY, and 1 to 12 for NIGHT, hence, as the axis of the time-piece performs its revolution with the card attached to it, the impurities, and the time when they happen, become exactly registered; and by changing these cards daily a perpetual register is obtained. The principle on which it acts renders the managing of it readily attainable; and its utility is so obvious, that perhaps it will eventually come into general use.

AN

INSTRUMENT FOR

ASCERTAINING

THE SPECIFIC GRAVITY OF GAS.

Another valuable addition to the apparatus relating to gas, for which the public is indebted to

Mr. Crosley, is a very simple and efficient contrivance for ascertaining the specific gravity of carburetted hydrogen gas, which he has accompanied with an appropriate Table for rendering the calculation easy and concise, at different temperatures and barometrical pressures. The following is a figure of the instrument, and the description and the Table annexed are copied from Mr. Crosley's.

As the Specific Gravity of CARBURETTED HYDROGEN GAS is one of the leading tests of it's illuminating power, the following easy method of ascertaining it is submitted for the use of those who are engaged in the management of Gaslight Establishments.

The figure represents the form of a flask, with an opening and cap at each end, which may be