A NEW INSTRUMENT FOB SCIENCE. 497 



Photography Applied to Astronomy. — M. Cornu has devised an im- 

 proved system of astronomical photography, the peculiarity of this method 

 consisting in the fact that it does not require any special instrument, any 

 telescope, and may at once be adopted for photographical observation by 

 means of a purely mechanical arrangement, which does not at all affect the 

 optical qualities of the instrument; the two lenses which compose the ob- 

 jective have merely to be separated to an extent depending on the nature of 

 the glasses, but rarely exceeding one and a half per cent, of the focal dis- 

 tance. This operation shortens the distance about six to eight per cent. 

 Theory and experience prove that the original achromatism of the visible 

 rays is transformed into achromatism of the chemical rajs, which is neces- 

 sary to the perfection of photographic images. Direct and precise measure- 

 ment has shown that this slight separation of the glasses does not cause 

 any aberration in the images, which, of course, is an essential. 



This method, it is stated, has succeeded perfectly at the Paris observatory, 

 with the lai-ge equatorial, the objective of which is about 15 inches in aper- 

 ture and about 29 feet in focal distance. By a very simple arrangement the 

 glasses can be separated, and the instrument may be employed for optical 

 as well as photographic observations. The photographic adjustment does 

 not present any inconvenience in the observation of faint stars, M. Cornu 

 stating that he easily observed Uranus and at least one of his satellites 

 without re-establishing optical achromatism. At the principal focus of this 

 instrument are obtained direct photographic images of the sun and of the 

 moon, measuring nearly 3.42 inches in diameter — images which might be 

 easily magnified b}' means of the eye-piece so as to give negatives of more 

 than 39 inches in diameter. 



A New Instrumenu' for Science. — There is now in operation in the lab- 

 oratory of Central Universit}^, Richmond, Ky., says the Louisville Courier- 

 Journal, an interesting apparatus that records in a beautiful manner the 

 motion of the earth in its hourly progress through space. It is the invention 

 of Prof. T. W. Tobin. The principle upon which the instrument is formed 

 is, that a delicately constructed pendulum will continue to oscillate in the 

 same direction as started, and preserving that plane, mark the movement 

 of the earth beneath it. The principle was demonstrated by Foucault, a 

 a philosopher, in 1851, was verified in Boston at the Bunker Hill monument, 

 and lastly again at Yale College. The apparatus hitherto employed has been 

 cumbersome, and the results obtained somewhat vague. The experiments, 

 nevertheless, bear historical interest, and are related in modern text-books 

 on physics. It has devolved on Kentucky to furnish the scientific world 

 with a finished and mathematical demonstration of this beautiful phenome- 

 non, together with the apparatus for producing the result so as to be proved 

 in a school-room or laboratory. The instrument is about six feet high, con- 

 sisting of an iron tripod and delicate pendulum. There is an index attached 



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