450 SCIENTIFIC RECORD FOR 1884. 



into work. The interval between two temperatures is represented not 

 by a difference but by a ratio, the ratio between the quantities of heat 

 received and rejected by a perfect engine working between these tem- 

 peratures. {J. Phys., February, II, iii, 53; July 1884, II, iii, 27V.; 



Pettersson has laid down the following principles with reference to 

 the measurement of heat: First, measurements of heat should be executed 

 at constant temperature, *. e., without the aid of thermometers ; second, 

 the amount of heat developed in calorimetric experiments should be 

 directly transformed into work and measured in absolute units ; third, the 

 principle should be applicable to the measurement of all kinds of ca- 

 loric energy, such as specific heat, radiant heat, the heat absorbed or 

 evolved in chemical reactions, &c. Several forms of apparatus are de- 

 scribed which the author has used for such measurements, including 

 the form finally adopted. (Nature, July, 1884, xxx, 320.) 



Guthrie has studied the thermal and corresponding volume-changes 

 attending the mixture of liquids, the substances used being alcohol, 

 carbon disuljihide, amylene, ether, chloroform, and benzene. (Phil. Mag., 

 December, 1884, V, xviii, 495.) 



Cailletet has constructed an apparatus for the continuous production 

 of intense cold, which consists of a closed steel cylinder containing a 

 coil of copper pipe projecting from each end. Two copper tubes are 

 screwed into the cylinder; one of these communicates with the author's 

 mercurial piston-pump, the other receives the ethylene, which has been 

 compressed by the pump and cooled by methyl chloride. In this way 

 a circuit is formed , in which the same quantity of ethylene is repeatedly 

 evaporated in the copjjer coil, producing intense cold, and then com- 

 pressed again by the pump, it being cooled sufficiently by the evaporation 

 of methyl chloride. (Science, April, 1884, in, 526.) 



Barbier has demonstrated Eegnault's principle between weight and 

 stem thermometers, that if they are in accord at two fixed points they 

 remain in accord at all temperatures, as follows : If the temperature 

 <° be defined by saying that 5,550™™ of mercury at 0° become 5,550+ 

 <™'" at P, then in the stem thermometer it will occupy at 0° 5,550™™ 

 of volume = «; and at t°, n-{-t volumes. In the weight thermometer, 

 containing all the mercury at 0°, t volumes will flow out at t^, leaving 



n volumes ; i. e., the fraction will flow out, and will remain- 



' ' n+t ' n+t 



The ratio of these values is — , which is proportional to t as in the 



n 



stem thermometer. Since ^ = -.pr--^ — , the two thermometers are di- 



cP — p 



rectly comparable with one another when c is made equal to B-5V0. (C. 



B., l^ovember, 1884, xcix, 70-2.) 



Mayenyon has devised an instrument, which he calls a thermogalvan 



oscope, for the purpose of rendering the expansion of wires visible at 



a distance, serving, therefore, as an indicator of temperature. It con- 



