PHYSICS. 451 



sists of a raetallic wire fixed at the ends, and connected at its middle 

 point with a cord passing over a jmlley above and having a counter- 

 weight below. When the wire elongates by heat, its center falls, rotates 

 the pidley, and causes an index to traverse a graduated scale. The ap- 

 paratus is very sensitive as a thermoscope, and by passing a current 

 through the wire it may be used as a galvanoscope. {J. Phys., Septem- 

 ber, 1884, II, III, 393.) 



Clodig has proposed to furnish steam-boilers with mercury thermom- 

 eters, the reservoir (which is of iron) being placed in the steam, while 

 the stem (which is' of iron within dnd glass without the boiler) passes 

 through the metal. The pressure of the steam compresses the reservoir 

 of the thermometer and increases the rise of the mercury in the tube, 

 thus acting as a manometer. {J. Phys., May, 1884, II, in, 222.) 



Browne has given a resume of the most important pyrometers at pres- 

 ent in use. In Siemens's instrument the temperature is determined from 

 the increase in the resistance of a platinum wire as the heat increases. 

 Tremeschiui uses the expansion of a thin plate of platinum which is 

 heated by a mass of metal previously raised to the temperature of the 

 medium, in order to determine the temperature. Trampler's pyrometer 

 is based on the differential exi)ansion of iron and graphite. The Gaunt- 

 lett instrument is similar, except that fire-clay is used instead of graph- 

 ite. Ducomet's pyrometer consists of a series of rings having progress- 

 ively lower melting points. These are strung on a rod, which is pushed 

 into the medium to be measured, the rings being pressed together by a 

 spring. When any ring softens it is pressed out, the column shortens, 

 and a simple apparatus shows the temperature. The instrument known 

 as the thalpotasimeter is based on the principle that the tension of a 

 saturated vapor is proportional to the temperature. A tube of metal 

 is partly filled with a liquid suited to the temperature to be measured, 

 and connected with a pressure-gauge. Ether is used from 100^ to 220° 

 F., water up to 680°, and mercury above this. Saintignon's pyrometer, 

 as improved by Boulier, depends on the water-current principle, the 

 temperature being determined by noting the amount of heat communi- 

 cated to a known current of water circulating in the place whose tem- 

 perature is desired. At Limoges and at Sevres this pyrometer has been 

 satisfactorily used for determining the temperature of the porcelain fur- 

 naces. {Nature, August, 1884, xxx, 366.) 



Von Baumhauer has contrived a modified form of thermo-regulator 

 for use with paraffin baths to render the temperature constant. It con- 

 sists of an air reservoir containing mercury, plunged into the paraffin. 

 As the temperature rises, the expansion of the air forces the mercury 

 up a central tube until it cuts off the flow of gas entering by a smaller 

 tube adju8ta,ble within the latter. (C. B., August, 1884, xcix, 370.) 



Ericsson has published a description of the sun-motor which he had 

 in operation in the summer of 1883, as the result of twenty years' experi- 

 ments. Its leading feature is that of concentrating the radiant heat 



