PHYSICS. 449 



Conservatory of Music is a middle 0, a true sixth below the normal A; 

 hence 261 vibrations. Hence the C fork used with an orchestra which 

 has A for its standard does not agree with this. Chickering's and Miller's 

 forks are C standards, a tempered sixth below the French A ; hence 

 258.7 vibrations. Thomas's present pitch is an A, a little sharper than 

 the French A. In Handel's time the C fork had 240.0 vibrations ; hence 

 the difficulty now experienced in singing old music. {Science, May, 1884, 

 III, 667.) 



Compton has devised a method for autographically recording the 

 vibrations of a tuning-fork in terms of the beats between it and a siren. 

 Three pens make records on a strip of chemical paper. The first marks 

 seconds, the second the revolutions of the siren, and the third the beats. 

 Since the first pen is connected to the back contact of a relay, and the 

 second to the front contact, both pens cannot record together ; and when 

 the coincidence is perfect, the siren mark is omitted. The beat record 

 is made by placing a membrane over the small end of a resonator, with 

 in adjustible platinum contact in the main circuit of a relay, the pen 

 being in the secondary- circuit. The adjustment is so made that when 

 a fork placed in front of the resonator beats with the siren, the circuit 

 is broken, the armature falls back and closes the secondary circuit, pro- 

 ducing a dash on the paj^er. The record, therefore, shows three sets of 

 marks : First, the beat dashes ; second, the siren revolutions ; and third 

 the seconds marks. From the two latter the i)itch of the siren is deter- 

 mined ; and this, with the two former, determines the pitch of the fork. 

 {Am. J. ScL, June, 1884, III, xxvii, 444.) 



HEAT. 



1. Production of Heat. — THermometry. 



Lippmann has objected to the thermometric scales in use as being 

 entirely arbitrary. Neither temperature nor intervals of temperature 

 are measurable magnitudes, in the proper sense of the word. To meas- 

 ure a quantity is to find its ratio to a magnitude of the same kind taken 

 as a unit. The only physical magnitudes cai)able of measurement are 

 those of which multiples can be constructed. But this is not true of 

 temperature, since intervals of temperature cannot be added. He sug- 

 gests, therefore, an absolute thermometric scale founded on the quantity 

 of mechanical work done by heat-engines. According to Carnot's prin- 

 ciple, the maximum efficiency is the same for all heat-engines working 

 between the same limits of temperature. If such an engine take a quan- 

 tity of heat, Q, from the source of heat and give up the quantity Q' to 



Q/ 



the refrigeral or, then the ratio -^r has a minimum value for a given in- 



terval of temperature, independent of the nature of the engine. The 

 temperature-interval is rei)resented by tliat fraction of a heat-unit which 

 is transferred to the refrigerator without having been transformed 

 S. iVlis. :« 1^|> 



