Analtfsis of Scientific Books. 397 



proved by its taking place equally under all circumstances, 

 even when the ships were firmly beset with ice ; nor was it 

 change of temperature, for not the least correspondence be- 

 tween its changes and those of the rates could be observed ; it 

 appeared, therefore, to Mr. Fisher, to result from the magnetic 

 action exerted by the iron in the ship, upon the inner rim of 

 the chronometer's balance, which is composed of steel. That 

 the iron of ships is magnetic is shown by its polarity, the whole 

 forming one large magnet, having its south pole on deck, 

 nearly amid-ships, and its north pole below; now when we 

 consider how easily the presence of any thing magnetical is de- 

 tected by the alteration of the rate of a chronometer, it is not 

 surprising that the ships' iron should exert considerable influence 

 upon them. Mr. Fisher concludes this paper by showing, 

 that magnets, placed near the steel-balances of watches and 

 chronometers, produce a very rapid acceleration in their rates 

 of going, in every position of the magnets, and with both poles. 

 Upon too near an approach of the magnets the watch is often 

 rendered useless. 



It seems, therefore, desirable that the use of steel should if 

 possible be avoided in the construction of the balances of 

 chronometers for sea use : the force of the balance-springs is 

 also probably affected by the same cause, for chronometers with 

 gold balance-springs, though more difficult to adjust, yet keep 

 the best rates at sea. 



v. On the Measurement ofSnowdon by the Thermometrical Barometer, 

 By the Rev. F. J. H. Wollaston, B.D. F.R.S. 



In this paper Archdeacon Wollaston gives an account of an 

 actual measurement made with the instrument which he has 

 described in the Philosophical Transactions for 1817; he ad- 

 verts to the calculations necessary in the measurement of con- 

 siderable heights by means of it, and compares his own resu is 

 with those of General Roy. The author makes the height of 

 Snowdon 3546.25 feet. 



