Intelligence and Miscellaneous Articles. 389 



so experienced an engineer as Mr. Clegg to present himself before 

 the public as the inventor of an instrument which he considers likely 

 to realize what appears to be so much required. 



The construction and action of this meter are based upon the 

 established facts, that the heat and light from the various kinds of 

 carburetted hydrogen gas are strictly proportionate to each other ; and, 

 by the application of that fact, in combination with an apparatus, act- 

 ing on the same principle as the differential thermometer of Leslie. 



By this apparatus will be measured most delicately the smallest 

 differences of heat, and consequently the consumption of gas will be 

 registered in proportion to its illuminating power. 



Let two hollow glass cylinders, each about one inch in diameter 

 and three inches long, be connected together in the centre of their 

 lengths by a hollow bent tube of the same material (being such as 

 will be afterwards described when treating of the mechanical ar- 

 rangements for a six-light meter, and delineated in the accompanying 

 figures). Let these cylinders and the connecting tube be perfectly 

 exhausted of air, and let as much alcohol be introduced as will nearly 

 fill one cylinder, leaving a vacuum in the other — or at least leaving 

 it without air, and with only such vapour therein as may arise from 

 the alcohol. Now as pure alcohol boils, in vacuo, at 56° of Fahren- 

 heit's thermometer, the smallest excess of heat above this tempera- 

 ture applied to the cylinder having the alcohol therein will cause the 

 liquid to evaporate, and, by its consequent elasticity, will drive the 

 spirit below the vapour into the colder cylinder ; and the velocity with 

 which the alcohol will be driven out from one cylinder to the other 

 will be in exact proportion to the quantity of heat applied, twice or 

 three times the cause producing twice or three times the effect, and 

 so on. For, let air or gas be heated to a uniform temperature (say 

 to 150° of Fahrenheit), and, when so heated, let it be directed to 

 impinge upon one of two glass cylinders (such as those above de- 

 scribed) with any given velocity ; if this velocity be doubled, then 

 double the quantity (or volume or body) of heat will be passed, and 

 consequently double the effect (that is double the velocity with which 

 the alcohol is driven) must be produced, such being an unerring and 

 natural law. Although twice the effect be thus produced, the tem- 

 perature of the air or gas has not been increased ; it is only the flow 

 or quantity which has been augmented ; and this must be what is to 

 be understood by quantity of heat. The best criterion of the sound- 

 ness of the above statement is, that these facts have been determined 

 from, and are founded upon, repeated and concurring experiments — 

 the only true source of philosophical induction. 



Such, then, being established, it became a leading principle ; and 

 the next step was to ascertain, by further experiments, how to apply 

 this scientific fact to the art of measuring the quantity of heat applied 

 to one of the above-described glass cylinders,and of registering the 

 same ; for this being accomplished, there was at once obtained an 

 apparatus, whereby may be determined the exact flow of air or gas in 

 a given time ; in other words, a gas-light meter, such as the present 

 instrument. The first consideration therefore was, how to heat a 

 given quantity of gas to a certain uniform temperature, for the gas 



