of measuring Time at Sea. 55 
I shall hereafter demonstrate more positively) to give the vi- 
brations of the balance the greatest freedom possible, ‘This 
is what I have practised in my machines. 
Article III. 
- Third cause of variations in watches—the manner in which 
. 
the balance is sustained, and the different situations in 
- which they are placed. 
It is clear that the weight of the balance occasions on the 
pivots that sustain it,a friction that is both variable and pre- 
judicial ; but much less considerable, when, the watch being 
Jaid flat, it is carried on the extremity of one of its pivots, 
than when, hanging, the weight of the balance is borne on 
the circumference of the two pivots: by what precedes, there 
follow causes of variations, greater or less, according to 
the size of the pivots, their polish, the polish of the holes, 
their depth, the oi] which is applied, the weight and size of 
the balance, the number of its vibrations, their magnitude, 
the length of the spiral spring, its form, &c. Experi- 
ence shows, in effect, that most watches, especially those 
which have dead escapements, lose when hung up. To 
correct this irregularity, we render the balance more weighty 
in that part of its circumference which is underneath when - 
the watch is hung up: but by this expedient we palliate the , 
evil rather than destroy it, and we render the watch more 
subject to vary by shocks and different motions, the effect 
of which to be done away requires (as we shall presently 
see) that the balance be throughout of equal weight. 
Article IV. 
Fourth inconvenience of watches, —they y lose in heat, and 
gain in cold. 
This effect arises in watches with a dead escapement, 
1st, From the different causes which render the vibrations 
of the regulator greater by heat: 2dly, Because the dimen- 
sions of the balance, and its spring, are augmented by it : 
3dly, From its diminishing the elasticity of the latter. From 
these united effects there results a variation, greater or less, 
according to the nature of the escapement, the length and 
D4 force 
