318 Magnesian Limestone • 
At present, 12 wine gallons of distilled water weigh exactly 100 
pounds avoirdupois. 
A hundred English wine gallons of common air weigh a pound 
avoirdupois. 
On the subject of labor of workmen, Dr. Young observes : 
In order to comoare the different estimates of the true force of 
x 
moving powers, it will be convenient to take a unit, which may be 
considered as the mean effect of the labor of an active man, work- 
ing, to the greatest possible advantage and without impediment ; 
this will be found, upon a moderate estimation, sufficient to raise 10 
pounds, 10 feet in a second for 10 hours in a day : or to raise 100 
pounds, which is the weight of 1 2 wine gallons of water, 1 foot in 
a second. 
For every minute that a clock varies in a day, a second pendu- 
lum must be altered 2-37 or .054 inch. A half second pendulum 
1-74 or .00134. 
Rain and Dew . — Dalton makes the mean for England and 
Wales 36 inches amounting in a year to 28. cubic miles of water, 
that is 7-12, and thinks that the Thames carries off 1-25 of the rain 
and dew that falls in England ; other rivers 8 times as much, mak- 
ing together 13. inches and leaving 23. for evaporation* 
MAGNESIAN LIMESTONE. 
Some time ago the honourable Richard Peters , of Belmont, near 
Philadelphia, requested I would take the trouble of analysing 
some limestones for the purpose of ascertaining the quantity of 
magnesia they might contain. In England, the impression among 
scientific men, in consequence of the experiments of Mr. Tenant, 
in Phil. Trans. 1790, are, that limestone containing a considerable 
quantity of magnesia, such as the limestone of York, in York- 
shire ; Bredon, in Leicestershire ; Matlock, in Derbyshire, and 
some other places, were unfavourable to agriculture. Mr. Tenant 
found that seeds sown in earth, sprinkled with lime made from 
calcareous limestone, vegetated very well, and the lime operated 
favourably : but when sprinkled with an equal quantity of lime, 
made from a stone that contained two parts of magnesia to three 
of pure lime, they did not vegetate* 
