436 PHILOSOPHICAL TRANSACTIONS. [ANNO 1/83. 



Professor Braun himself took great pains to investigate it, but, for want of per- 

 ceiving the consequences of the metal's great contraction in becoming solid, went 

 very wide of the truth. This source of error did not escape the penetration of 

 other philosophers, several of whom declared their opinion that the degree of 

 cold necessary for the congelation of quicksilver could hardly be determined by 

 freezing a thermometer filled with that fluid. But Mr. Cavendish and Dr. Black 

 were the gentlemen who suggested an adequate method of obviating the dif- 

 ficulty, so as to ascertain the point in question with certainty and precision. 

 Reasoning on the well-known fact, that a quantity of water continues at the same 

 temperature from the moment it begins to freeze till the whole is become solid, 

 they very justly concluded that the same would hold good with regard to quick- 

 silver ; and Mr. Cavendish confirmed this inference by experiments with metals 

 of easy fusion, in which he found a thermometer keep at the same degree all the 

 time they were passing from a fluid to a solid state. Hence it was proposed, that 

 a small thermometer should be placed in some quicksilver to be frozen ; which 

 sinking pretty regularly till the congelation began, and remaining stationary till 

 it should be complete, would thus show the degree of cold at which this effect 

 takes place. 



Though the methods proposed by Mr. Cavendish and Dr. Black were essen- 

 tially the same, yet there was some difference in the apparatus they recommend- 

 ed ; and as the former gentleman got his executed in London and sent out to 

 Hudson's Bay, it was that which Mr. Hutchins employed in performing most of 

 his experiments. These have not only confirmed the preceding observations re- 

 lative to the solid state into which quicksilver can be brought by cold, its metalline 

 splendour and polish when smooth, its roughness and crystallization where the 

 surface was unconfined, its malleability, softness, and dull sound when struck; 

 but have also clearly demonstrated, that its point of congelation is no lower than 

 — 40°, or rather — 39°, of Fahrenheit's scale ; that it will bear however to be 

 cooled a few degrees below that point, to which it jumps up again on beginning 

 to congeal ; and that its rapid descent in a thermometer through many hundreds 

 of degrees, when it has once past the above-mentioned limits, proceeds merely 

 from its great contraction in the act of freezing. These and the other conse- 

 quences reducible from Mr. Hutchins's experiments have been so exactly pointed 

 out in the present volume by Mr. Cavendish, the real author and first mover of 

 the whole business, that nothing remains but to add a few supplementary re-, 

 marks. 



Though in two of Mr. Hutchins's thermometers the quicksilver sunk exceed^ 

 ingly Iowj to — 450° or near — 500°, there is reason to believe he did not in any 

 instance obtain the extreme term of contraction, since Professor Braun, in some 

 of his last experiments, brought the mercury in one thermometer to — 544°, and 



