SCIENTIFIC EXPERIMENTAL APPARATUS. 433 



2. A standard ohm, r.nd two boxes of resistance coils running from one 

 to five thousand olim?;. 



3. An induction coil made in the horseshoe form and pro^^ded with 

 iron phites for armatures. The two induction coils comprise a resistance 

 of 12,0U0 ohms. 



4. Galvanometer for absolute measure. — Maker: Edelmann, Munich. 

 A short coil minor instrument, adapted for absolute measures by certain 

 methods. Eesistance, C ohms. 



5. Thomsoii's rcjlecting galvanometers. — One of 5,880 ohms resistance — 

 a differential instrument. 



One of 6 ohms resistance, adapted for heat measures. 



G. Thomson^s quadrant electrometer. — Made by White, of Glasgow. 



7. Cathetometer. — Maker: Perreaux, Paris. Eeads by vernier to 2- 

 lOOths of millimetre, or by micrometer to 1-lOOth of a millimetre. Focal 

 length of objective, 13 centimetres; magnifying i^ower of telescope 30 

 times. 



8. Dividing engine. — Maker: Perreaux, Paris. Screw, Gl centimetres 

 long. Pitch of screw, one-half of a millimetre. Micrometer reads to 

 one four-hundredth of a millimetre. Instrument adapted only for grad- 

 uating tubes and scales, or for comparison of graduations. 



9. Large spectroscope. — Designed by Professor J. P. Cooke, of Harvard 

 University. Two trains of prisms. One of nine bisidphide of carbon 

 prisms of 45°. One of nine flint-glass prisms of 45°. Graduated circle 

 reading to 10 seconds, also a micrometer eye-piece. Magnifying power 

 of telescope, 10 times; focal length of objective, 4G centimetres; aperture, 

 5.5 centimetres. 



10. Reading telescope and scale. — On brass leveling stand. Telescope 

 l^rovided with two objectives : one for short, the other for long, distances. 



Magnifying i^ower for long distances, 22 times. 



Magnifying power for short distances, 30 times. 



Focal length of the objective for long distances, 30 centimetres. 



Focal length of the objective for short distances, 23 centimetres. 



Aperture of objectives, four centimetres. 



Harvard University. — AsxRONOMicAii Observatory. 



(In charge of Professor E. C. Pickering.) 



LIST OF INSTRUMENTS NOT IN CONSTANT USE AND AVAILABLE FOR 



RESEARCH. 



1. East transit circle, by Troughton and Simms, of London. Aperture 

 of telescope, 4-^ inches; focal, length, 5 feet. Described in Vol. I, pt. 1, 

 of the Annals of the Observatory, p. 46. 



2. West equatorial, by Alvan Clark & Sons, of Cambridge. Aperture 

 of telescope, 5^ inches ; focal length, 7^ feet. Described in Vol. VIII 

 of the Annals of the Observatory, p. 31. 



S. Mis. 59 28 



