432 SCIENTIFIC EXPERIMENTAL APPARATUS. 



In connection with these instruments the following, belonging to the 

 Rumford professor, are also available : 



1. A large spectroscope with telescope and collimator of 4.75 centimetres 

 aperture and 5.5 centimetres focal length. Magnifying power from 8 to 

 60 times. Object-glasses by Fitz, of New York. Six hollow prisms of 

 (^rbonic disulphide — glass faces 6x8 centimetres — arranged on Mr. 

 Rutherfurd's plan, so that all the prisms are constantly in the position 

 of minimum deviation. The stand, observing telescope, and prisms of 

 this instrument may be used in connection with the long collimator 

 belonging to the Rumford cabinet. 



2. A large hollow prism, with angle of 30° — glass faces 6x8.5 centi- 

 metres — for Professor Gibbs's solution of phosphorus and sulphur in car- 

 bonic disulphide. See American Journal of Science and Arts, Vol. IV, p. 

 6, 2d series. 



3. Two flint-gluss prisms — faces 8.5x5 centimetres — which may be 

 used singly or together. Angles of 60°. 



4. Professor Gibbs^s double or compensating prism for the study of ab- 

 soqjtion spectra. See American Journal of Arts and Sciences, Vol. IV, p. 8. 



5. Five gratings ruled with Mr. Rutherfurd's engine : 



No. 1. Ruled on speculum metal, 6,480 lines to the inch. Ruled sur- 

 face 2.1x2.8 centimetres. Metal a little tarnished. 



No. 2. Ruled on glass and silvered, 8,640 lines to the inch ; 7,021 lines 

 uiwnaruled surface 2x2.7 centimetres. Covering-plateof glass cemented 

 with Canada balsam. 



No. 3. Ruled on glass for spectra by transmission, 6,480 lines to the 

 inch. Ruled surface 1.7x2.7 centimetres. 



No. 4. Ruled on glass for transmission of light, 12,960 lines to the inch. 

 Ruled surface 1.3x2.7 centimetres. 



No. 5. Ruled on glass and silvered; 13,321 lines on a space 19x24 

 centimetres, with covering-glass cemented by Canada balsam. 



KirchhofPs, Angstrom's, and Mascart's maps of the spectrum. 



Mr. Rutherfurd's original photographs, together with the German 

 lithographic reproduction of the same. 



Mr. Rutherfurd's recent photographs takeu with the diffraction si)ec- 

 tmm. Thalen's map of the absorptive bands of iodine vapor. 



The thermometers by Fastr6, of Paris, carefully compared with an air 

 thermometer reading from 0° to 100° C. 



Harvard University. — Department of Physics. 



(In charge of Professor John Trowbridge.) 



1. Edelmannh instrument for measuring horizontal and vertical in- 

 tensity of earth's magnetism. 



The peculiarity of this instrument consists in its allowance of a long 

 suspension, and in its torsion head. 



