300 Miscellaneous Intelligence. 



be found that the image of the slit is distorted to a greater or less degree; far- 

 ther examination shows that the glass plate has been slightly bent by the 

 hardening of tlie glue, and in those of my preparation the curvature was con- 

 cave. If two or more such prisms are used for the production of a spectrum 

 a certain amount of confusion is always seen among the fixed lines; plates of 

 glass of even ' of an inch in thickness are constantly affected in this manner, 

 .and unless the evil be removed the prisms are of no great value. 



After many vexatious failures I have perfectly corrected this difficulty m 

 a very simple manner: the prisms are finished in the way above described 

 with glass of good quality, then a few drops of olive oil are placed on one of 

 the faces and a plate of truly plane glass laid on it ; the oil spreads out and is 

 held in position by capillary attraction, the four corners are then secured by 

 four drops of melted wax and resin. Optical contact is thus secured, and the 

 Blight curvature corrected : each face is in turn thus dealt with. The substi- 

 tution of Canada balsam for oil I have also tried, but it is impossible under 

 several months to offer any opinion on its merits. Large prisms of bisulphid 

 of carbon thus corrected, while remarkably cheap, approach, I think, a degree 

 of optical perfection not attainable by the best flint glass prisms yet produced, 

 for even if the flint prism is of equal size with that of bisulphid of carbon, and 

 optically unexceptionable, the fact still remains that the dispersive power ol 



With three such prisms of 60°, and a flint glass prism of 45°, a.ray of light 

 IS refracted about 180°, a spectrum furnished which with the power I employ 

 is ten feet long, the lines being as clear and sharp as those in an engraving 



this apparatus I have discovered many lines not laid down in Kirchhoff's new 



new lines in the interior of the line D, making in all three fine lines which are 

 enclosed in this double line. 



Encouraged by the excellent performance of these prisms, I am now engaged 

 is to be effected by from eight to ten of these prisms, carrying thus into eff^' 

 a suggestion made by Kirchhoff some few weeks ago in his paper on the soiar 

 spectrum. 



Before closing this letter one practical point remains to be alluded to: it is 

 not essential tliat the plates of glass should have truly parallel sides, provide 

 .that the plates are cut in such a manner that Ujeir plane of refraction coincides 

 with the plane of refraction of the prism. Sincerely, 



Troy. Au^. 7tb, 1662. O. N. RoOO- 



8. Ascent of the Volcano of Candarave, Peru, (about lat. 18°S., lo"- 

 ^^'^ "^ ^ ■■ " '" ■ Stuah^^Church, Esq., Civil Engjer 



and Lieut. Governor o 



a single day, we started at 2 o'clock ot) SiTnday to seek lodgings at tiw 



base. The Governor was backing out at the last moment, when «e found 



us directions about the best road, and ursred the Governor to go ^^'^'J."^' 

 The Indian villagers however gathered about us, smiling at our makiog 

 * While in MuDich in 1857. T requested Prof. Steinheil to give me a Ainj g 

 " ■'t't^rerar?mpn,'ctiS;'£lgh"'Sisper.lJ 



billable d) 



