416 TRANSACTIONS OF THE 



tions given to the rays in passing out of the water into the atmosphere, 

 caused by the ripple on the surface, where the refraction takes phice ; 

 when these obstructions are removed, we can distinctly see the bottom. 

 The tube of the marine telescope screens the eyes from reflection, because 

 the water comes in contact with the glass plate, so that the person looking 

 through the tube, sees distinctly the objects at the bottom. 



Light passing through salt water, loses half of its intensity for every 

 fifteen feet through which it passes. 



A new reflecting telescope has been constructed by Mr. Lyman of Lenox, 

 Massachusetts, the tube of which is composed of thick Russia iron. Up to 

 1852, this telescope, in point of optical power, was in advance of anything 

 before achieved in this covinti-y. It separated double stars, distant from 

 each otlier half a second of arc. 



Yale College has a telescope made by Dolland, of London ; it has a focal 

 length of ten feet, and an aperture of five inches. The object glass is 

 perfectly achromatic, and for objects that require a fine light it is a superior 

 instrument. 



In 1852, an achromatic refracting telescope, manufactured by Clark, of 

 Boston, was presented to Williams College. It is mounted equatorially, 

 and has a clock movement. The sixth star in the trapezium of Orion, has 

 been seen by it, which is certainly an indication of its superiority. 



The Hudson Observatory, in Ohio, has an equatorial telescope, with a 

 transit circle and clock ; it was made by Simms, of London, and clock by 

 Molineux, and has a mercurial pendulum. 



The Philadelphia High School have an equatorial telescope, made by 

 Merz and Mahler, of Munich. It is of eight feet focal length, and six 

 inches aperture, with clock-work movement, and has a variety of powers 

 to 480 with micrometers. This instrument was the most superior that had 

 been imported from Europe up to 1840, and introduced Munich to 

 America. 



The Philadelphia Observatory became celebrated at home and abroad for 

 having furnished 43(5 moon culminations, and 120 star occultations, together 

 with a series of observations for latitude. 



At West Point we have a large equatorial telescope, made by Lerebours, 

 of Paris. It is a refractor, of eight feet focal length, and six inches aper- 

 ture, and is moved by clock-work. 



The Washington Observatory have a refracting telescope, made by Merz 

 and Mahler, of Munich. It has a repeating filar micrometer, with eight 

 eye pieces, magnifying from 100 to 1,000 times. The cost of this instru- 

 ment was $6,000 ; its object glass is valued at §3,600. 



The Georgetown Observatory has an equatorial instrument, made by 

 Simms, of London, at a cost of $2,000. 



Cincinnati Observatory was so fortunate as to secure, through the me- 

 dium of Professor Mitchell, a superior object glass, twelve inches aperture, 

 found at Munich, which has been pronounced, by those who ought to know, 



