SCIENTIFIC EXPERIMENTAL ArPAEATUS. 437 



read by estimation to tenths. The instrument is arranged especially for 

 measurement rather than for graduation. 



3. Spectrometer, by Clark. Furnished with five 60° and one 30° jjrisms, 

 the latter silvered on its rear surtace. A greater or less number of prisms 

 can be used at will. Face of prisms 5.7 centimetres by 7.3 centimetres. 

 Focal length of telescope, 70 centimetres; diameter of object-glass 5.2 

 centimetres. Diameter of circle, 43.5 centimetres, reading to 10" by 

 verniers. Smaller angles are measured by spider-line micrometer. The 

 same telescope serves as collimator and observing telescope, the method 

 of reflection from the silvered siu'face of the glass being used. 



4. Diffraction grating, ruled by Chapman on Mr. Eutherfurd's engine. 

 17,250 lines to an inch ; 30,000 spaces. Area of ruling, 4.5 centimetres 

 square. 



2. Two prisms of quartz, QO'^, faces 5.5 centimetres by 4.0 centimetres. 

 Also various prisms of flint glass and heavj" glass. 



Eaton's direct-vision prism of glass and carbon disulphide. Small 

 direct-vision prisms of glass. 



G. Polarimeter of Professor Pickering, for sky-polarization. See Froc. 

 Am. Acad., Vol. IX. 



7. Wheatstone^s bridge, by Elliott, measuring from .001 to 1,000,000 

 ohms. 



8. Thomson's long-coil galvanometer. — Eesistance, 3,000 ohms. Thom- 

 son's short-coil galvanometer for thermo-electrical work; resistance, 

 G-10 ohm. 



9. B. A. divided metre bridge. 



10. Tangent galvanometer. — 36 coils, 26 centimetres radius. Gaugain 

 tangent and sine galvanometer. Cosine galvanometer. 



11. Induction coil, by Eitchie, giving 6-inch spark. 



Colujmbia College, New York. 



(In charge of Professor O. N. Rood.) 



1. Neicman's standard barometer ; diameter of tube, 0.6 inch; reads to 

 1-500 inch. 



2. GrunoixPs spectrometer. — Focal length of lenses, 14 inches ; diameter 

 of circle, 9 inches ; aperture, 1.3 inches ; reads to 10 seconds. 



3. Cathetometer. — Length, 800™™; focal length of telescope, 10 inches ; 

 aperture, 1.1 inches. Provided with extra object-glass for reading at 

 short distances. 



4. WihVs pliotometcr, simi)le construction, diameter of circle, 6 inches. 



5. Apparatus for measuring the velocity of sound in rods of wood by 

 means of longitudinal vibrations. Described in American Journal of 

 Science, Vol. XVII. 



0. Magneto-electric machine, by Wallace (no motor). 

 7. Ruhmkorff^s diamagnetic apparatus. 



