244*. .Dr. .blagden’s Hijlory of 
in thefe refearches neglected fuch a principal objedt of enquiry ; 
on the contrary, Profedor biuun himfelf, as hath been already 
mentioned, took infinite pains to invedigate it, but, for want 
of perceiving the confequences of the metal’s great contraction 
in becoming folid, went very wide of the truth. This fource 
of error did not efcape the penetration of other philofophers, 
feveral of whom declared their opinion that the degree of cold 
neceffary for the congelation of quickfilver could hardly be de- 
termined by freezing, a thermometer filled with that fluid. But 
Mr. cavendish and Dr. black were the gentlemen who fug- 
gefted an adequate method of obviating the difficulty, fo as to 
afcertain the point in queftion with certainty and precifion. 
Reafoning on the well-known fad, that a quantity of water 
continues at the fame temperature from the moment it begins to > 
freeze till the whole is become folid, they very judly concluded 
that the fame would hold good with regard to quickfilver; and 
Mr. cavendish confirmed this inference by experiments with 
metals of eafy fuiion, in which he found a thermometer keep 
at the fame degree all the time they were paffing from a fluid - 
to a folid date. Hence it was propofed, that a frnall thermo- 
meter fhould be placed in fome quickfilver to be frozen ; which 
finking pretty regularly till the congelation began, and remain- 
ing dationary till it fhould be complete, would thus fhew T the 
degree of cold at which this effect takes place. 
It is not at all furprifing, that both the above-mentioned 
gentlemen fhould have fuggeded the fame method, without the 
lead communication of each other’s fentiments. Mod difcove- 
nes follow' fo clofely upon a certain date of' advancement in 
every Icience, that, under the prefen t general diffufion of know- 
ledge, fimilar ideas mud be expected to occur about the lame 
time to fuch perfons as are engaged in fimilar purfuits. When 
the fruit i9 come to a certain degree of ripencis, more than one 
