SCIENTIFIC EXPERIMENTAL APPARATUS. 431 



with parallel spider lines, and with a separate collimating eye-piece. 

 The spectrometer stands ui)on a plate of metal which can be made to 

 revolve, so that measurements by repetition are practicable. The instru- 

 ment is in perfect adjustment, and has everything necessary for the de- 

 termination of wave lengths and of indices of refraction. In connection 

 with it the Rumford cabinet possesses : 



2. Two gratings, Nos. 1 and 2, ruled on speculum metal by D. C. Chap- 

 man with Mr. Rutherfurd's engine. One of these, No. 1, has 8,G48 lines 

 to the inch and a ruled surface (4.3 cm. x 5.2 cm.). The other has 17,296 

 lines to the inch and the same ruled surface as No. 1. They may be ad- 

 justed to the spectrometer above described by plate-holders constructed 

 by William Gruuow, of New York, with all necessary requirements for 

 the measurement of wave lengths. 



3. A collimator, l.G metres focal length and G.5 centimetres aperture, 

 mounted upon a stand and specially adax)ted to the study of the extreme 

 visible red and violet ends of the si>ectrum. Object-glass by Alvan Clark 

 & Sons. A quartz lens of same focal length is to be added to this in- 

 strument from the workshop of Steeg & Renter, in Homburg vor der 

 Hohe, as well as a telescope with quartz objective and eye-piece for 

 observing the ultra-violet spectram. 



4. A porte-lumicre, by Duboscq. A Foucault's heliostat has been 

 ordered, and may be expected in the course of the summer. 



5. Yierordfs apparatus for measuring the intensity of light correspond- 

 ing to any part of the visible spectrum. Telescope and collimator 25 

 centimetres focal length. Apertures, 2.8 centimetres and 2.1 centimetres. 

 The instrument was made by Schmidt & Haensch, of Berlin, and is com- 

 plete with prism and colored glasses. 



0. A direct-vision spectroscope, with two sets of 9 prisms each. Set 1 

 contains 4 prisms of carbonic disulphide and 5 of crown glass. Set 2 

 consists of 4 prisms of flint and 5 of crown. The length of the instrument 

 is 60 centimetres. It is provided with a scale telescope, and the observ- 

 ing telescope has the usual angular motion. Tliis instrument is also by 

 Schmidt & Haensch. 



7. An inductoriunij by Apps, of London, giving a 4-inch spark. 



8. Three thermometers, by Baudin, of Paris, reading to .01 degree cen- 

 tigrade. 



No. 1. Reading from OP to 12° centigrade. 

 No. 2. Reading from 12° to 23°. 

 No. 3. Reading from 23° to 35°. 



In tliese instruments the weights of the bulbs, stems, and contained 

 mercury are given. 



9. Edison''s tasimeter, made by Patrick & Carter, of Philadelphia, and 

 adjusted by Mr. Edison. See Afnerican Journal of Arts and Sciences^ 

 3d series. Vol. XVII, p. 52. A galvanometer suited to this instrument 

 will be found in the cabinet in charge of Professor Trowbridge, together 

 with the requisite batteries and Wheatstone's bridge. 



