PHYSICS. 473 



in place of the mercury, a driving wheel producing rapid interruption. 

 When a tuning fork is supported so as to be capable of rotation before 

 a resonance case, it gives a strong resonance or a weak interference 

 tone according to its position, the latter being higher. On rotating, 

 the former becomes the higher and the dissonance increases. A reso- 

 nance interference pipe is made by connecting the nodes of an open pipe 

 with a rubber tube. By pressing this tube the pitch of the pipe is altered. 

 ( Wied. Beibl, No. 3 ; Nature, June, xxvi, p. 138.) 



HEAT. 



1. Production of Heat ; Thermometry. 



naga has investigated the variations of temperature which are pi^o- 

 duced when metallic wires are submitted to traction. The wire was 

 stretched horizontally, one end being attached to the vertical arm of a 

 bent lever, the tension being produced by weights on the horizontal arm. 

 The temperature was measured by a thermo-electric couple, one of whose 

 elements was the wire itself, and the other a wire of another metal 

 wound round the first. A steel wire 1.6°"" and a wire of German silver 

 1.5™™ in diameter were used, the auxiliary wire being of iilatinum 

 Q Qgmm thick. With a tension on the steel wire of 21.715 kilograms the 

 increase of temijerature was 0.1054°; the tension of 17.134: kilograms 

 on the German silver wire gave 0.1429°. The heating with the latter 

 wire was proportional to the stretching weigh c. From the data thus 

 obtained, llaga determined the mechanical equivalent of heat and ob- 

 tained for the steel wire 437.8, and for the German silver 428.1. ( Wied. 

 Ann., V, XV, p. 1; J. Phys., September, II, i, p. 425.) 



Ilolman has suggested a simple, accurate, and ready method of cali- 

 brating thermometers, which requires one-third to one-half the time 

 of the method of Neumann, with equal accuracy, and is fully one-third 

 shorter and somewhat more accurate than that of Pickering. Two cali- 

 brations of a Baudin thermometer, using threads of mercury of 3 and 

 S''™ respectively, each with only one series of observations, requiring 

 an hour and a half for comi^letion, gave results whose average differ- 

 ence at 9 points was 0.04™™, the arithmetical sum of the extreme differ- 

 ences being 0.12™™. {Am. J. Sci., April, III, xxiii, p. 278.) 



Michelson has described an air thermometer whose indications are 

 independent of the i^ressure of the air. It consists of a glass bulb 4<=™ 

 and a stem 2™™ in interior diameter, the bulb containing dry air at a 

 pressure of about 100™™ of mercury, this air being separated from the 

 upper portion of the tube by a column of mercury about 100™™ in length. 

 This mercury remains above the air, notwithstanding the large diameter 

 of the bore, owing to the resistance of the meniscus to deformation. 

 The space above the mercury is a vacuum. The pressure of the air in 

 the bulb is constant and equal to that of the column of mercury above 

 it. (Am. J. ;SVL, August, III, xxiv, p. 92.) 



