1805.] ( 149 ) 



PROCEEDINGS OF LEARNED SOCIETIES. 



ROYAL SOCIETY OF EDIN- 

 BURGH. 



DR. Charles Hope has laid before 

 this Society an account of experi- 

 ments, with obfervations, upon the con- 

 tiaftion of w?ter by heat at low teinuera- 

 tures. It has been long known that heat, 

 when applied to witer at the temperatme 

 of 32", caufes a diminution in the bulk 

 of the fluid. The waier contracts, and 

 continues to contracf, with the increale of 

 temperature, till it reach trie 40th or 41 It 

 degree. Bet-.veen this point and the 4id 

 or 43d, it fufTers fcarcely any perceptible 

 change ; but when heated beyond this, it 

 expands in proportion to the heat commu- 

 nicated. The objedl of Dr. H.'s Paper 

 is to prove, by a fet of new experi- 

 ments, that this op:n,Dn with regard to 

 water is founded in tru'h. 



Dr. H. relts his conclufions on fix expe- 

 riments, the la((^ of which is as follows : 



Ex. VI. — " I filled the jar with water of 

 the temperature jgi^^, the air and I'upport 

 being 39°." 



Thermometers were fufpended near the 

 bottom, and jult below the furJace of the 

 fluid in the jar. 



A mixture of fnow and fait was iniro- 

 dQced into the bafin about the middle 

 part. 



Botiom. lop. Air. 

 At commencement, . 39.5 39.5 39' 

 In 10 minutes, . . 39+ l'i-\- 

 In 25 ditto, . . . 39-j- 36.5* 

 In35ditto, ... 39 36 — 

 In 55 ditto, ... 39 35 

 An hour and 10 min. 39 — 34-h 

 An hour and 35 ditto, 39 — 34^ 

 Two hours, . . . 39 — 33-i- 



" This experiment (fays Dr.H.) (haws, 

 that when a portion in the mid lie of a co- 

 lumn of water at temperature 39. "5 is 

 co-.led, the colder fluid rifes, and docs not 

 defcend through the warmer niafs, and 

 prefents the uncqi'ivocal demonliratioiis, 

 that water of the tempeiatuve 39^' is ac- 

 tually expanded liy 1 , ling lieat." 



The author concludes, that the general 

 import of his expeiimtnts is, that water 



• Ice at this time began to be fSrnicd on 

 tjtelidc of the vclFcl. 



which is ice-cold, or a fe'.v degrees warm, 

 er, when bested, becomes Ipecifically hea- 

 vier ; — that water of 40" when heated be- 

 comes fpecifically lighter ; — .that water 

 above 40*, by the lofs of heat, or by cold, 

 is rendered fpecifically heavier ; — ind that 

 water below 40" is by the fame caufe ren- 

 dered fpecifijnily lighter. Hence heat in 

 low temperatures caules water to contrail, 

 and at lupciior temperatures to expand \ 

 and Dr. H. thinks, that the point" at 

 which the change in the conltitution of 

 this fluid in relation to heat takes place, 

 lies between 39-|'' and 40'. 



Mr. Profeflbr Playfair has prefented 

 to this Society " A Comparlfon ot lome 

 Obfervations on the Diurnal Variations of 

 the Barometer, made by M, Lamanon in 

 Peyroufe's Voyage round the World, 

 with thofe mads at Calcutta by Dr. Bal- 

 four." 



The agrcerrcnt between thefe is r;- 

 marka'jle. Dr. Balfour found, duiin-j 

 the whole lunation, in which he obfervtd 

 the barome er from hilt hour to haif- 

 hour, that ihe mercury cont.intly fell from 

 JO at night to 6 in the morning ; and 

 from 6 to 10 in the mornir.g it role : from 

 10 in the mon.inH; to 6 at night it fell 

 again ; a ,d lylt'y role from 6 to jo at 

 nigtir, Tiie grcTleff heiglit is therefore 

 at 10 at night and to in the morning, and 

 the leaft at 6 at night and 6 in the morn- 

 ing. 



Tlie only difference between this and 

 the refult of M. Lamanon's oblervaticns 

 is, th»I, accoiding to the latter, the mini- 

 mum is fta'cd to have happened about 4, 

 inliead of 6. 



Ac-ording to Dr. Balfour, the varia- 

 tii-ns of the barometer are conneflecl with 

 the reciprocaiicins of the f.a and land- 

 winds during the day and night. But the 

 probability of this fuppofition is dertroyed 

 by the obfervations of the French navigi- 

 tors. Thefe ol)!<:rvations were nia:e .00 

 far ou' at lea to leave room lor fiip,i' fing 

 that the land-winds had any ii.flue. cr in 

 the phe.-.omena to which they refer. It is 

 at khe fame time doubtful wheihrr thiie 

 |-he:.'imena can be afcribed to t'ae atino. 

 fpiicrical tides produced by the Sun ard 

 Moon, as the ebbing and fl.')j>'ing of the 

 niticury in the barometer appears lu have? 



