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, in, 63; 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 tem^jerature, i. 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 disulphide, amylene, ether, chloroform, and benzene. {Phil. Mag., 

 December, 1884, Y, xviii, ^95.) 



CaiUetet 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 copper coil, producing intense cold, and then com- 

 pressed again by the j)ump, it being cooled sufficiently by the evaporation 

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



Barbier has demonstrated Regnault'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 

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

 <"•" at t°, then in the stem thermometer it will occupy at 0° 5,550"^™ 

 of volume = w; and at f^, n-]-t volumes. In the weight thermometer, 

 containing all the mercury at 0°, t volumes will flow out at <o, 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 



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



cP — p^ 



rectly comparable with one another when c is made equal to b-bVo- {(^• 



B., iS'ovember, 1884, xcix, loQ.) 



Mayengon 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- 



