286 Mr. Walker's Observations on the 
any climate at any season, to as certain, and almost as easy a 
process, as that I originally set out with, for the freezing of 
water (Phil. Trans. Vol. LXXVII.) ; viz. by previously cool- 
ing the materials in one mixture, to produce the effect in a 
second. It may very likely appear to some, that I have been 
too minute in a few particulars ; yet as perhaps experiments 
of this kind, all circumstances considered, are inferior to few 
in the delicacy required to make them succeed completely, I 
trust I shall be excused by those who choose to repeat them, 
particularly such as are not in the habit of making experi- 
ments of this kind ; especially if it secure them from an un- 
successful attempt, and that, perhaps, without being able to 
account for it. 
Oxford, 
March ist, 1795. 
It is very well known, that vitriolic ether will produce suffi- 
cient cold by evaporation to freeze water; this circumstance 
is noticed by many, and several different methods have been 
proposed, particularly one by Mr. Cavallo, with a very in- 
genious apparatus for the purpose (Phil. Trans. Vol. LXXI.) ; 
nevertheless, as l am upon the same subject, and the following 
experiments differ, as well in the effect produced as in the par- 
ticular mode of conducting them, from any I have met with, 
I have ventured to mention them. 
June 29th, 1792, temperature of the air 71 0 , I sunk a ther- 
mometer (the bulb being covered with fine lint tied over it, 
and clipped close round), by dipping it in ether, and fanning 
it, to 26°; then, by exposing the thermometer to the brisk 
thorough air of an open window, to 20°; and again, by using 
