430 scientific experimental apparatus. 



American Academy of Arts and Sciences, Boston, Mass. 



Applications for use must be made to Prof. Joseph Lovering, chair- 

 man of the Eumford Committee, Cambridge, Mass. 



1. Meyerstein^s spectrometer. — Aperture of collimator and telescope, 3.3 

 centimetres ; magnifying power of telescope 18 times ; graduated circle 

 reads by means of two micrometers to two seconds. Instrument intended 

 to be used with a diagonal eye-piece for obtaining reflection at right 

 angles to the reflecting surface. It is not well adapted for measuring 

 indices of refraction, except by the special method for which the instru- 

 ment was designed. 



2. Large holloio prism of glass, with movable glass faces, held in their 

 places by springs. Angle 00°. 



3. Prof. J. Trowbridge's electro-dynamometer. — Instrument for measur- 

 ing the strength of powerful electric currents such as are produced by 

 dynamo-electric machines. Mean radius of fixed coils 153.3 millimetres. 

 Instrument described in Proceedings of American Academy of Arts and. 

 Sciences, October 9, 1878. 



4. Thomson's galvanometer, resistance 6 ohms. 



5. Micrometer-level, constructed by Alvau Clark & Sons. Telescope, 

 45 centimetres focal length and 4 centimetres aperture, in Y's moved by 

 vertical micrometer screw, reading to 0.3" by estimation of tenths. In- 

 tended also for use with eye-piece micrometer. One division of level 

 tube (0.15 cm.) =8.7". Transverse level and slow motion for rotating 

 telescope in Y's. Horizontal finding circle graduated to degrees. 



6. Light micrometer-level. — Telescope 21 centimetres focal length and 

 25 centimetres aperture, in Y's moved by vertical micrometer screw, read- 

 ing to 1.4" by estimation of tenths. One division of level tube (0.25 

 cm.) = 1.8". Horizontal finding circle graduated to degrees. 



7. Microscope-tube and accessories, specially designed for measuring 

 spectrum photographs. Also a standard plate of 24ths of an inch j rulings 

 on glass by Prof. William A. Eogers. 



8. A large double induction coil of the form devised by Prof. John 

 Trowbridge. 



9. Apparatus for the determination of the mechanical equivalent of heat. — 

 Devised by Prof. Henry A. Rowland, of Johns Hopkins University, and 

 now in his charge. 



Harvard University. — Eumford Cabinet, Cambridge, Mass. 



(In charge of Professor Wolcott Gibbs.) 



1. A spectrometer by Brunner Freres, of Paris. The instrument has 

 a single graduated circle 10 centimetres radius, reading by two verniers 

 to 5 seconds of arc, and by a micrometer eye-piece to about 2 seconds. 

 The telescope and collimator have 33 centimetres focal length, and 3.4 

 centimetres aiJerture. The micrometer is provided with cross and also 



