THERMOMETER AND PYROMETER. 



ment more convenient, by making one 

 reservoir for the liquid and for the air 

 at the bottom of the tube ; and thus the 

 thermometer might be conveniently 

 dipt in a fluid, or applied to any body 

 for ascertaining its temperature. " The 

 thermometer," he says, " being made 

 by the insertion of a cylindrical pipe of 

 glass (open at both ends) into a phial 

 or bottle, and by exactly stopping with 

 sealing wax, or very close cement, the 

 mouth of the phial, that the included 

 air may have no communication with 

 the external, but by the newly men- 

 tioned pipe."* If a portion of any liquid 

 sufficient to cover the lower extremity 

 of the pipe, be contained in the bottle, 

 it is obvious, that the expansion of the 

 enclosed air will elevate the included 

 liquid in the cylindrical pipe ; and this 

 liquid will again descend on the contrac- 

 tion of the enclosed air \Jig. 4,5. Mr. 



Fig. 4. Fig. 5. 



Boyle likewise showed that no depend- 

 ence could be placed on the indications 

 of open air thermometers, under different 

 degrees of atmospheric pressure; and 

 he states, that on plunging the bulbs of 

 different thermometers in liquids of very 

 different specific gravities, as mercury 

 and water, thej liquor in the stem stood 

 at unequal heights, though both had 

 been long exposed to the same tempera- 

 ture. 



The Florentine thermometer was 

 about that time introduced into Eng- 

 land, and duly appreciated by both 

 Boyle and Hooke. The specimen seen 

 by these philosophers was filled with 

 colourless spirit, but they made use of 

 spirit of wine, tinged by cochineal, 

 ( Of a lovely red ;" and, says Boyle, 



us pleasant to see how many inches 

 a mild degree of heat will make the 



Works of Hon. Robrt Boyle, folio, vol. ii, p. 



tincture ascend in the cylindrical stem of 

 one of these useful instruments."* Boyle 

 was fully aware of the imperfection of 

 the scales hitherto applied to the ther- 

 mometer, and sought to discover a re- 

 medy. He proposed to obtain a fixed 

 point in the scale, by marking the height 

 of the liquid in the stem of the instru- 

 ment, when the ball was placed in 

 thawing oil of aniseeds ; a point 

 which he preferred to that of thawing 

 ice, because the former could be readily 

 obtained at any time of the year. His 

 method of making two or more com- 

 parable thermometers, however, would 

 be found extremely difficult, if not im- 

 possible, in practice; it is best ex- 

 plained in his own words. " For if you 

 put such rectified spirit of wine into a 

 glass, the cavity of whose spherical, 

 and that of its cylindrical part, are as 

 near, as may be, equal to corresponding 

 cavities in the former glass, you may 

 by some heedful trials, made with 

 thawed and recongealed oil of aniseeds, 

 bring the second weather-glass to be 

 somewhat like the first ; ^and if you 

 know the quantity of your spirit of 

 wine, you may easily enough make an 

 estimate, by the place it reaches to in 

 the neck of the instrument, whose capa- 

 city you also know, whether it expands 

 or contracts itself to the 40th, the 30th, 

 or the 20th part, Sec. of the bulk it was 

 of, when the weather-glass was made."t 

 Boyle mentions that an " ingenious 

 man""% had proposed the freezing of 

 distilled water, as a fixed point in the 

 scale of thermometers ; but he himself 

 evidently gives the preference to the 

 congealing point of aniseed oil. Dr. 

 Halley proposed to regulate the scale by 

 the uniform temperature of such a ca- 

 vern as that under the Observatory of 

 Paris, or the point at which spirit 

 boils ; and he also suggests the fixing 

 of the scale from the boiling of water. 

 This point he considered as an invari- 

 ably fixed one, not liable to alteration 

 from external circumstances ; and the 

 same idea was entertained by Amon- 

 tons. With a single point so fixed, the 

 method attempted by Boyle, Halley, 

 and Hooke was to calculate the pro- 

 portion of the stem to the ball, and thus 

 to determine the increase in bulk of the 

 whole liquid, by a certain temperature. 

 Dr. Hooke describes a method of ob- 

 taining this by comparing the expansions 



* Works, vol ii. p. 249. 

 f Works, vol. ii. p. 247. 

 | He undoubtedly alludei to Hooke, 



