VOL. XLIT.] PHILOSOPHICAL TRANSACTIONS. 407 



a thermoscope of that range will be sufficient for common uses; and therefore 

 one fitted with a brass rod will answer these purposes. 



In large furnaces for running down ores, or melting great quantities of metal 

 together, it is not possible to place such an instrument ; but then in lead and 

 tin there may be small outlets contrived, into which some of the melted metal 

 may be permitted to flow, and remain in contact with the same body of metal 

 within, where the instrument may be placed; and for placing a thermoscope in 

 iron, copper, or glass furnaces, there may be a place contrived, which shall not 

 open into the furnace, but have the thickness of a stone or brick left between, 

 on which the instrument may be placed; and though in such a situation it will 

 not measure the actual heat within the furnace, it will always give the relative 

 or comparative heat in the like circumstances at different times, and so show how 

 to regulate the heat within. 



Though a chemist shall have one of these instruments to measure the heat he 

 may have used in any experiment, and have noted down the several degrees made 

 use of, and the time each lasted, he still labours under another difficulty, which 

 is the not being able to command any required heat, and that it shall last a cer- 

 tain required time, unless it be below that of boiling water, which may be pro- 

 cured and continued by various contrivances of lamps, either of spirits, or of 

 oil ; but how to continue a fire for ] 2 or 24 hours together, without attendance, 

 which shall continually keep quicksilver boiling, lead in fusion, or may be let 

 down so low as not to exceed the heat of sunshine, and then be raised again, 

 and that without letting out the fire, or moving the vessels, may seem almost 

 impracticable ; but by an improvement of the furnace the ancient chemists called 

 their athanor, he thinks it may be effected. 



Remarks on the foregoing paper. By the Rev. Stephen Hales, D. D. p. 693. 

 — What [ intended to do, says Dr. Hales, was only this, viz. to get a leaden 

 wire, of such a size and strength as to bear its own weight, to have it as long as 

 the longest gun-barrel I could procure, and to have it sustain a lever as above; 

 then to pour boiling water into the barrel, for a long time, till the lever rises no 

 more; the water to have vent at the bottom, yet so as to have the gun-barrel 

 always full of water; the breech-pin to be out, and the leaden rod to rest on a piece 

 of wood set upright, according to the course of its fibres, not sidewise. To give 

 at the same time to a mercurial thermometer the heat of boiling water. Then 

 to take the freezing point of the leaden and mercurial thermometers; and after- 

 wards to graduate all the intermediate degrees, fi:om the mercurial thermometer 

 on the leaden thermometer, as they occur. Thus a standard thermometer may 

 be made to graduate others by; but I need not now set about it, since that is 

 done above. 



" All solid bodies are observed to contract with cold." I hare found that 



