14 



instrument by which he may ascertain the time for rating his 

 clocks with far greater accuracy than by the ordinary means of 

 the sun-dial and meridian line — the instrument may be con- 

 structed at a very trifling cost and made to serve the purposes of 

 a level also. 



40. Eye Piece with Cavalld's Pearl Micrometer. — By the Rev. 

 N. S. Heineken. This is intended to obviate the objections to 

 the application of this simple micrometer to the reflecting 

 telescope. 



41. New Self-registering Thermometer. — By 

 John Brown and Son, Opticians, &c. Grey-street, 

 Newcastle. — The construction of this instrument 

 will be understood by the annexed diagram ; A is 

 a glass tube filled with pure spirit of wine; B is a 

 continuation of the same but much smaller, which 

 is to be about half full of quicksilver to support 

 the spirit in the long tube; upon the quicksilver at 

 G is a float supporting the wire C, which wire has a 

 knee or bend in it with a small eye, which runs upon 

 the fixed wire D, carrying an index or pointer ; E h 

 the scale which must be made experimentally. The 

 action of the instrument is obvious. If any change 

 takes place in the bulk of the spirit the quicksilver 

 is also affected, and with the silver the ivory float G carrying 

 the index or pointer, which shews at once the degree of tempera- 

 ture upon the scale; this is the simple action of the thermo- 

 meter. To make it register, the two light indexes or pointers F 

 move upon the wire D, their own friction keeping them where- 

 ever they are placed. To set it the pointer F below the thermo- 

 meter's index must be pushed close up to it, and the pointer F 

 above, pushed down it ; and it is evident that if any change of 

 temperature takes place the thermometer"'s index will move the 

 registering index either above or below, and leave it there, 

 thereby shewing the extreme rise and fall of the thermometer in 

 any given time. The action of the air upon the quicksilver is 

 also provided against. 



