144 ANNUAL OF SCIENTIFIC DISCOVERY. 



loses half its intensity for each 15 feet through which it passes, we 

 must from this cause alone, at a certain depth, lose sight of objects of 

 the brightest lustre. The freedom of the water from all muddy parti- 

 cles floating in it forms an important element in the effective use of 

 the water-telescope ; for these act in exactly the same way, in limiting 

 our vision through water, as a fog does through air. In a trial made 

 with the instrument on the coast of Scotland, the bottom (a white one) 

 was distinctly seen at the depth of 12 fathoms ; and on a black rocky 

 bottom, objects were so distinctly seen at 5 fathoms under water, that 

 the parts of a wreck were taken up, the position of which was not 

 known previous to its use. In the Western British Islands the water- 

 telescope is in general use for seal-shooting, where it is sometimes 

 merely a wash-tub, with a piece of glass fixed in the bottom. The 

 seal when wounded always seeks the bottom, whence he never rises 

 after death until washed ashore by the action of the sea ; but by the 

 simple contrivance mentioned, he may be found and raised by grappling 

 irons. Robert Stevenson, a number of years ago, even made use of 

 the water-telescope for examining the sand-banks in the River Tay, 

 where the clearness of the water was much obstructed by muddy par- 

 ticles. He obviated the difficulty arising from this source by making 

 the tube of considerable length, placing the glass at the lower end, 

 and lowering the whole until within a short distance of the bottom. 

 The tube, thus acting as a coffer-dam, set aside the dirty water, and 

 enabled the bottom to be seen. 



IMPROVED TELESCOPE. 



MR. NASMYTH described to the British Association a new arrange- 

 ment of the reflecting telescope, by which great additional comfort is 

 afforded to the observer. It reflects the rays from the smaller mirror, 

 which is convex, upon a diagonal mirror, placed near the larger spec- 

 ulum, by which they are sent off through the trunnion. The telescope 

 is mounted on triangular supports, and on one side is placed a chair 

 for the observer, the whole being fixed to a turn-table, and so con- 

 structed that it can be turned in any direction by the observer, without 

 removing his eye from the glass. Such a degree of steadiness is thus 

 attained, that the observer can have a star or other object in view for 

 a whole hour. The telescope can in a few seconds be changed into a 

 Newtonian, by removing the diagonal mirror, and placing it at the 

 trunnion. 



IMPROVEMENT IN THE MICROSCOPE. 



A NEW method of viewing opaque objects under the highest power 

 of the microscope (the $ and ^ inch object-glasses) has recently been 

 devised by Mr. Brooke. This is effected by two reflections. The 

 rays from a lamp, rendered parallel by a condensing lens, are received 

 on an elliptic reflector, the end of which is cut oft* a little beyond the 

 focus ; the rays of light converging upon this surface are reflected down 

 on the object by a. plane mirror attached to the object-glass, and on a 



