WATCHES. 
45 
Cheaper watches, purporting to have compensation balances, and 
the best balance springs, may be obtained from many shops; but it 
will often be found (when too late to replace them) that they are not 
all they profess to be, that they have never been properly adjusted, 
and are, in consequence, so affected by change of position and temperature 
as to be useless for scientific purposes. 
Persons not having much experience with watches frequently expect 
too much from them, and are under the impression that if a watch 
maintains a good rate in England, this rate will remain unchanged in 
the tropics, where the heat is great. This is not the case, as the rates of 
all watches, no matter how carefully compensated they may have been, 
will undergo a change if subjected to great variations of temperature, 
and it is absolutely necessary that frequent observations should be taken 
for determining the rate of the watch under these altered circumstances 
by one of the methods given, pp. 153,154,162 and 163. It must also be 
remembered that if a watch is allowed to run down, it will probably 
take quite a different rate when again set going, and that the rate of 
a watch when lying down almost always differs slightly from what it is 
when carried, hence the necessity for the traveller to take the time of his 
observations for error and rate, while carrying the watch in the same 
manner he intends to do during his journey. 
