442 SCIENTIFIC EXPERIMENTAL APPARATUS. 



36. Rulimlcorff's apjparatus for diamagnetism. Made by Eulimkorff, of 

 Paris. 



37. Electric clocks beating seconds from regulator. 



38. RoivlandJs standard of electro-magnetic induction. — Three coils on 

 brass cylinders which can be placed accurately on toj) of each other. 

 See American Journal of Science. Mutual potential of coils with unit 

 current 3,775,500; 2,561,974; 2,051,320, «&c., on the cm, grm. second sys- 

 tem. 



39. Telescopes^ scales^ and mirrors. — Silvered brass millimetre scale by 

 Brown & Sharp. Mounted telescope by Steinheil, objective 4.0 centi- 

 metres diameter, with three oculars, giving powers of 20, 40, and 80. 

 Unmounted telescope by Steinheil, objective 2.7 centimetres diameter, 

 and 3 oculars. 



Mounted telescope and paper scale by Meyerstein ; objective, 2.7 cen- 

 timetres diameter. 



40. Thin mirrors and plain parallel glasses by Steinheil. The mirrors 

 give a perfect image with the highest magnify%7ig poioer. 



Thomson^s replenisher on large scale for use with electrometer, Holtz 

 and friction machines, Leyden jar batteries, Geissler tubes, «&;c. 



HEAT. 



41. BoidanWs instrument for comparing the mercurial with the air tJier- 

 mometer between 0° and 100° C. Constructed by Schneider, instrument 

 maker at the university. Eeadiugs seldom differ more than 0.02° or 0.03° 

 C. at any one point, especially up to 40° C, and a change is contemxjlated 

 which will much improve it. 



42. Boivland's instrument for comparing thermometers from 0° to about 

 300° C. Constructed by Schneider. Accurate to about 0.1° C. 



43. BegnauWs air thermometer, Golaz, Paris. 



44. Jolhfs air thermometer, by Berberich, Phys. Inst. Univ. of Munich. 



45. Eegnaulfs apparatus for expansion of gases, both at constant press- 

 ure and constant volume, also Eegnaulfs form of Eudberg's apparatus, 

 Golaz, Paris. 



46. BegnauWs a2Jparattis for tension of vapors, mdlnding: a. The boiler; 

 I). The reservoir for comi)ressed air ; c. A rotary pump for compressing 

 gases ; d. Mercurial manometer. Maker, Golaz-, Paris. 



47. BegnauWs apparatus for specific heat of solids, Golaz, Paris. 



48. BegnauWs hygrometer with aspirator, Golaz, Paris. 



49. Thermometers, about 30 or 40, principally by Baudin, Paris, and 

 Geissler, of Bonn. Many of these have been compared with the air 

 thermometer as well as with standards by Fastre, Casella, or from Kew. 

 The thermometers up to 40° C. undoubtedly represent the air thermome- 

 ter more accurately than any so far constructed, and are supposed to 

 agree with it to about 0.01° C. They have been compared with it eight • 

 times during about one year or more. The error in calorimetric investi- 



