*$o6 Mr. hutchins’s Experiments for afari airing 
frequently with the bulb of the thermometer ; and if the cold 
be fufficiently ftrong, it will begin to congeal by coming thick 
and broafy like an amalgam. As foon as this is obferved, the 
thermometer fhould be examined without lifting it out of the 
congealing mercury ; and I have no doubt, that in every expe- 
riment, thus made, with the fame mercury, the inftrument will 
always point to the fame degree, provided it has been made 
and graduated with accuracy. 
I am, DEAR sir, 
Your faithful humble fervant, 
JOSEPH BLACK. 
To Mr. Andrew graham, Edinburgh. 
Thermometers 
