Page:Popular Science Monthly Volume 10.djvu/592

the present state of our acquaintance with the configuration of its surface, is not generally understood. When, however, the attention of astronomers is more generally directed to the study of the lunar surface, Science will he greatly the gainer, as it is there that the past and future of our earth is to be learned.

 

SIZE OF THE PRINCIPAL TELESCOPES IN THE WORLD.

IN Les Mondes, January 20, 1876, appeared a list of the principal telescopes of the world, with their apertures and focal lengths. It was defective in regard to its enumeration of American telescopes, and in other respects, as all such lists must be. We have compiled from it, and from other sources available, a larger list, which is itself manifestly incomplete, but which will give a better idea of the number of telescopes available, or soon to be available, for astronomical purposes. It is a melancholy fact that the return from so many instruments, that is, the interest from so much astronomical capital, is not so great as it should be, and it suggests the question as to whether future benefactors of American colleges, for example, will not do better to provide astronomers to use the telescopes already constructed than observatories in which to put new ones. In the second column, the first name is that of the maker of the objective or speculum, the second that of the engineer who mounted the telescope.

I. Reflectors.

"One French inch = 12 Paris lines; one English inch = 11.26 Paris lines; one metre = 443.30 Paris lines.

OWNER OR DIRECTOR, AND OBSERVATORY.	Constructed by	APERTURE.			FOCAL LENGTH.			Remarks
		English Inches, etc.	French Inches.	Metres	English Feet etc.	French Feet etc.	Metres.
Lord Rosse, Birr Castle	Rosse	6 ft.			55 ft.
Wm. Herschel, Slough	W. Herschel	4 "			40 "			Out of use.
Lassell, Liverpool, etc.	Lassell	4 "			37 "			Destroyed.
Ellery, Melbourne	Grubb	4 "			32 "
Le Verrier, Paris	Martin, Eichens			1.20			7	Silvered glass
Lord Rosse, Birr Castle	Rosse	36 in.
Tisserand, Toulouse	Foucault			0.80				Silvered glass.
Stephan, Marseilles	Foucault, Ei- chens			0.80			4.8	Silvered glass.
H. Draper, near N. York	H. Draper	28 in.			13 ft.			Silvered glass.
Lassell, Maidenhead	Lassell	24 "			20 "			Metal.
W. & J. Herschel, Slough and Cape Good Hope	W. & J. Herschel	15 "						Several mirrors.
H. Draper, near N. York	H. Draper	15 "
Maclean, Turnbridge Wells	With & Brown- ing	15 "
Pritchard, Oxford	De la Rue	13 "			10 ft.
Worthington and Raven- dell, Manchester	With & Brown- ing	13 "
Hirst, New Zealand	Browning	8½						Silvered glass.

and many others.