400 PHILOSOPHICAL TRANSACTIONS. [aNNO 1747. 



posed losing their cohesion, they become fluid ; but no experiments have yet been 

 made, which determine whether solids, exposed to cold beyond certain degrees, 

 will cease to contract any more. 



The learned Dr. Muschenbroek, prof, of astronomy at Utrecht, and f.r.s. 

 has lately invented a very ingenious instrument, which he calls a pyrometer, and 

 which Dr. Desaguliers has made some improvements on * ; a full description of 

 which he has given in his course of Experimental Philosophy, vol. i, p. 421, &c. 

 By this instrument the elongation of rods of several kinds of metals, by the ap- 

 proach of a certain number of flames of a spirit-lamp, and likewise their as 

 sudden contraction, on the extinguishing one or more of those flames, is ren- 

 dered sensible to the eye: which sufficiently evinces the matter of fact, and puts 

 it beyond all doubt. 



From the property of bodies contracting and expanding in cold and heat, have 

 all thermometers been constructed, that have ever been made use of, to observe 

 and compare the different degrees of Heat, either in our atmosphere, or in other 

 bodies. The most simple and most sensible of any, is that aerial thermometer 

 described by Mr. Boyle, in his new experiments and observations touching cold. It 

 consists of a glass bubble, with a very slender stem, not thicker than a raven's 

 quill. The bubble is left full of air, and a few drops of water being conveyed 

 into the stem in an erect position, will there remain suspended to a certain height; 

 but, by the least addition of heat, the air in the bubble expanding will push the 

 water up higher; or, by the approach of cold, the air contracting, the water will 

 fall lower in the stem. This instrument may be of use in small degrees of heat, 

 and in cold, till the water begins to freeze, when it becomes useless. 



The next in order of sensibility, is that first invented by Cornelius Drebbel of 

 Alcmar, and improved by Boerhaave. It consists of a hollow glass lens, joined 

 to a stem of a larger size than in the preceding, and a basin into which the end 

 of the stem is inverted. The air in the lens must be so much rarefied, and the 

 stem being inverted into a tinged liquor in the basin, the liquor will rise up some 

 way in the stem ; then, by the application of heat to the lens, the liquor in the 

 stem will be pushed down, and by cold the liquor will rise up. This instrument 

 will give notice of the smallest changes in the air ; but it cannot be immersed into 

 any liquid for chemical experiments, unless the stem be made much longer, and 

 bent down in form of a syphon: and even then it would be very unhandy, and 

 like the preceding would never serve for any degree below what would freeze the 

 liquor made use of, nor for any above what would force out the confined air 

 through the liquor in the basin. Besides, both these instruments, being subject 

 to the pressure of the atmosphere, they are not proper, without comparing the 



• This instrument hath since been greatly improved by that ingenious watch-maker Mr. John 

 EUicot, ».».». See Phil, Trans. N" 443.— Orig. 



