THERMOMETEK. 



Dp2 



6 



5 

 4 

 4 

 3 



2 

 2 

 I 

 O 



O 



|- Heats o 



f the air in lummcr. 



eats of the air in fpring and autumn. 



eat of the air in the winter. 



Water begins to freeze. 



Phil. Tranf. Abr. vol 



4 

 146! 



100 

 88 



85 

 64 



58 



56 



Oifervations by Dr 



part 11. 

 Hales's Thermometer. 



55 

 54 

 50 

 38 



From 

 to 



30 s 



20 



10 



From 

 to 

 From 

 freezing 

 point 

 to 10 

 i8 



31 

 29 



26 



24 

 21^- 



19 

 16 1 



«4 



12 



9 



o 



Anfwers to the heat of boiUiig water. 

 f Heat of water on which floating wax begins 

 \ to melt. 



Hotteft funfhine in 1727. 

 f Scorching heat of a hot-bed of horfe-dung, 

 \ and alio the heat of blood in high fevers. 

 r Heat of the blood of animals ; whence the 

 < heat of the blood to that of boihng water 

 (_ is as 14.27 to 33. 



Heat of urine. 

 r Due healthy heat of a hot-bed of horfe-dung 

 J in February, that of the open air being 17", 

 ) and nearly the bofom heat, and heat for 

 (_ hatching of eggs. 

 Heat of milk from the cow. 

 External heat of the body. 

 Common noon heat in the fun in July. 

 Mean heat of the air in the ftiade in July. 

 May and June heat ; and the molt genial heat 

 for moft plants, in which they flourilh and 

 grow moft. 



■ Autumnal and vernal heat. 



Winter heat. 



Temperate point. 



The moft kindly heat for melon-thiftlc. 



ananas or pine-apple. 



pimento. 



euphorbium. 



cereus. 



aloe. 



Indian fig. 



ficoides. 



oranges. 



myrtle. 



Frelh water juft freezing. 



Hales's Statical EfT. vol. i. p. 58, &c. 



For other fimilar obfervations, fee Frebzing Mixture, 

 and Heat. 



See on the general fubje£l of thermometers, Martine's 

 Effays, Medical and Philofophical, printed at London in 

 1 740, 8vo. Defaguliers's Exp. Phil. vol. ii. p. 289, &c. 

 Mufchenbroeck's Int. ad Phil. Nat. vol. ii. p. 625, &c. 

 ed. 1762. De Luc's Recherches fur les Modifications de 

 I'Atmofphere, torn. i. part ii. c. 2. NoUet's Legons de 

 Phyfique, torn. iv. p. 375, &c. 



TimRMOMETERS for particular Ufes. In 1757, the right 

 hon. the earl of Cavendifti prefented to the Royal Society 

 an account of a curious conftruftion of thermometers, of 

 two different forms ; one contrived to fhew the greatefl de- 



gree of heat, and the other the greateft cold, that may 

 happen at any time in a perfon's ablence. The firft confifts 

 of a cylinder of gl.ifs joined to a tube, and differs from the 

 common fort only in having the top of the ftem drawn 

 out into a capillary tube, which enters into a glafs ball C 

 {Plati XVI. Pneumatics, fig. ii.) joined on to the ftem at 

 the place where it begins to be contraded. The cylinder, 

 and part of the tube, arc filled with mercury, tlie top of 

 which fliews the common degrees of heat as ufual. The 

 upper part of the tube above the mercury is filled with 

 Ipint of vvme, and fome of the fame liquor is left in the ball 

 C, fo as to fill it almoft to the top of the capillary tube. 



When the thermometer rifcs, the fpirit of wine will be 

 driveti out of the tube, and will fall into the ball C. When 

 the thermometer finks again, as the fpirit cannot be returned 

 back from the ball, the top of the tube will remain empty, 

 and the length of the empty part will be proportional to the 

 fall of the thermometer. Confequently, by means of a 

 proper fcale, the top of the fpirit of wine will fhew how 

 many degrees it has been higher than when obferved, which 

 being added to the prefent height, will give the greateft de- 

 gree of heat it has been at. To fit this thermometer for 3 

 new obfervation, it is neceflary to fill the upper part of the 

 tube with fpirits, by inchning the inftrument till the fpirits 

 in the ball C cover the end of the capillary tube ; for if the 

 cyUnder is then heated, by applying the hand to it, or by 

 the flame of a lamp held at fome diftance, till the fpirits riie 

 to the top of the tube, and run over into the ball C, and is 

 then fufTered to cool in the fame pofition, the tube will re- 

 mai.i full of fpirits, and the thermometer will be fitted for a 

 new experiment. 



The fcale of degrees at top, which fliews the defeent of 

 the thermometer from the higheft point it has arrived at, 

 ought not, in ftriftnefs, to be the fame at all times of the 

 year ; for thefe degrees exceed the common degrees of heat 

 pointed out by the top of the mercury, as much as the co- 

 lumn of fpirit of wine expands, and therefore are greateft 

 when that column is fo ; i. e. when the greateft heat to 

 which the inftrument has been expofed is leaft. A difference 

 of 30 degrees of Fahrenheit's fcale, in the greateft rife of 

 the thermometer, v^ould require the fcale to be altered one 

 fixtieth part ; and the error arifing from making ufe of tlie 

 fame fcale, will be about one-fixth of a degree, if the ther- 

 mometer is obferved when it has fallen ten degrees. 



In the thermometer here defcribed, the bore of the tube 

 is about 0.027 inches ; and one inch of it contains two grains 

 of mercury, and anfwers to about ten degrees, the cylinder 

 containing about 2280 grains. When the fcale of degrees 

 is large, the cyhnder muft be of confiderable fize. The 

 quickfilver in the ball C ferves to fupply the tube, in cafe 

 any of it fhould be driven into the ball by the thermometer's 

 being expofed to too great a heat. 



If the weight of the mercury be thought inconvenient, it 

 may be avoided by the conftruftion m fig. 12. where the 

 bottom of the tube is bent fo as to point upwards, and is 

 joined to a ball A, which communicates with a cylinder 

 placed above it. It is in all other refpefts the fame as the 

 former inftrument. It is filled with fpirits of wine and mer- 

 cury ; the quantity of the latter being fufficient to fill the 

 whole tube and the ball A. 



The thermometer for ftiewing the greateft degree of cold 

 that happens in any place during the time the inftrument is 

 left in it, is reprefented in ^^. 13. The tube is bent into 

 the fliape of a fiphon, of unequal legs, ftanding parallel to 

 one another; the top of the fhorter leg is bent to a right 

 angle, and opens into a ball A, which, by means of a fhort 

 bent tube on the oppofite fide, communicates with a cylin- 

 3 T 2 der 



