SCIENTIFIC EXPERIMENTAL APPARATUS? 439 



Table in center has a gradnation G.O centimetres radius, reading by ver- 

 niers to v. Aperture of objectives of telescope and collimator, 3.9 cen- 

 timetres ; focal length, 35.0 centimetres ; power, 13. The angle between 

 lines of collimation of telescope and collimator may be read by small 

 circle to single degrees. 



3. StemheiVs spectroscope. — The clear aperture of train, including two 

 CO^ prisms, is 4.0 centimetres. Focal length of collimator and telescope, 

 32.5 centimetres ; powers, 8, 12, &c. Photographic scale. 



4. Silbernia>in''s heltostaf, &g. — This instrument, by Duboscq, has two 

 mirrors 18.0 centimetres by 9.0 centimetres, one silver under glass and 

 the other silver. Also, porte-lumiere. 



5. Janiinh interferential rcfractometer, with tubes 100 centimetres long, 

 for the study of refraction in gases, and a glass trough 20 centimetres 

 long for liquids, by Duboscq. 



6. Complete apparatus for the study of phenomena of interference, by 

 Duboscq. 



7. PliotograpMc apparatus. — Objective G.l centimetres aperture, and 

 about 40 centimetres focal length for plates; 10x12 inches, by Steinheil. 

 Dark room, collection of chemicals, and everything necessary for exj)eri- 

 ments on the subject. 



8. BecquereVs phospkoroscope, by Duboscq. 



9. Polarizing apparatus, from Steeg; also from Duboscq. 



10. A])paratus for producing monochromatic light of any color. Do- 

 signed by Hastings and made by Schneider. 



11. Prisms, gratings, &c. 



a. Hollow prism from Meyerstein; aperture, 0.1x5.2 centimetres. 



b. Hollow prism from Steinheil; aperture, 2.2 centimetres. 



c. Thallium glass prism from Steinheil; aperture, 4.8 centimetres. 



d. Two flint glass prisms from Steinheil; aperture, 4.7 centimetres. 



e. Crown glass prisms from Steinheil; aperture, 4.8 centimetres. 

 /. Two quartz prisms from Steeg; faces, 3.4x3.0 centimetres. 



g. Iceland spar prism; faces, 2.6x2.2 centimetres, by Steeg. 



h. Two rock-salt prisms, faces, 5.0x4.0 centimetres, by Steeg. Also 

 rock-salt lens. 



i. Large Nicol's prism, largest diagonal G.5 centimetres. Also a num- 

 ber of smaller ones. 



j. Gratings on speculum metal, 4.3x3.9 centimetres, with 8,048 lines 

 to the inch, and 4.4x4.4 centimetres, with 17,396 lines to the inch, and 

 a smaller glass grating, with 8,648 lines to the inch, all by Chapman 

 with Eutherfurd's engine. 



Kirchoif's, Angstrom's, and Eutherfurd's maps of the solar spectrum. 



I'. Old telescope by DoUoud. Objective about 4 inches diameter and 

 6 feet focal length. 



ELECTRICITY AND MAGNETISM. 



The distinguishing feature of the apparatus for these subjects is its 

 accuracy and the determination of the constants in absolute measure. 



