458 Miscellaneous Intelligence, 



dows brought as near tog-ether as possible, and even made to 

 touch or over-lap ; or that, when this cannot be done, the observa- 

 tion should be made from a point equidistant from the two sha- 

 dows. As to the shadows by transmission, the apparent variations 

 of intensity are so great for small changes in the position of the 

 eye, as to render the method altogether inapplicable. — Bull. Univ. 

 A. viii. 248. 



10. On the apparent Decomposition of White Light by a Reflect- 

 ing Body when in Motion. — The following experiment is described in 

 the MSS. of M. Benedict Prevost and published by M. P. Prevost. A 

 ray of solar light being introduced into a darkened chamber, is to have 

 a square piece of white paper about two inches in the side, passed 

 across it perpendicularly to the direction of the ray. The light 

 reflected by the paper, instead of being white, will present a small 

 white central portion, surrounded by the seven principal colours, 

 nearly in the order of the prismatic spectrum. When a red surface 

 is used instead of a white one, the decomposition of the light is 

 still more complete. When the paper has a slight blue tint, the 

 effect is less perfect than with the white paper. With a black sur- 

 face no colours appear, but a sort of smoky shade towards the 

 middle. A single passage of the paper is sufficient, but it is neces- 

 sary that it pass entirely through the ray, no part remaining in it. — - 

 Bib. Univ.— Bui. Univ. A. viii. 248. 



11. On the Barometer. — The following are conclusions at which 

 M. Bohnenberger has arrived relative to the barometer: i. The 

 surface of mercury in a tube 14.5 lines in diameter, is slightly 

 rounded at the edge; but, at the distance of two lines from the glass, 

 capillary depression disappears, and the surface is level, ii. The 

 mercury in a tube 5.8 lines in diameter, is convex over the whole 

 surface, the depression being .035 of a line. iii. The depression is 

 generally less in a vacuum than in the air, so that a syphon baro- 

 meter gives results too high, and the more so as the tube is smaller. 

 iv. Barometers constructed with tubes five lines in diameter, do 

 not require tapping to cause them to assume their proper height ; 

 and comparatively slight blows easily make the mercury rise too 

 high in tubes of a smaller diameter. — Annal. der Phys. und Chem. 



12. Easy Method of reducing Barometrical Observations to a 

 Standard Temperature^ by S. Foggo. — The expansion of mercury 

 deduced by the different philosophers who have examined it, is given 

 below; omitting the results of Sir G. Shuckburgh, as being rather 

 loo far from the mean of the others. 



Expansion of mercury, from 32° to 212° F. 



De Luc l-56th 



Lavoisier and Laplace l-55.22th( , ^r a<m\, 



Halstrom l-55th ["■ean. l-55.43th, 



Dulong and Petit l-&5.5th 



