1817.] Experiments on boiling Tar. 111 
Therefore H = 212 x 17:46378 — 11°463874 = 212 x 
6°00004 = 1272-008 fathoms. 
The difference between the two results, which is very inconsider- 
able, arises from the proportional parts being calculated on the 
supposition that the amounts, as well as the logarithms, or years 
corresponding to them, increase in an arithmetical progression. 
This, though in no case strictly true, will seldom lead to an error 
of half a fathom in the altitude, a degree of accuracy which is 
certainly greatly within the limits, furnished by the physical data of 
the problem. A practical rule for finding the height in fathoms may 
be given in the following words :— 
Divide the height of the barometrical column at the lower station 
by its height at the upper ‘station, extending the division as far as 
the data admit; search for the quotient among the amounts of 12. 
at five per cent. compound interest, and the years corresponding to 
it being multiplied by 212, will be the difference of altitude be- 
tween the two stations in fathoms. 
On the whole, though the method which I have proposed for cal- 
eulating heights by barometrical measurements must often be more 
tedious and intricate than the ordinary method by logarithms, it has 
this important advantage, that all the elements of the calculation 
may be laid down on a small slip of paper, or obtained in a few 
minates by the involution of 1:05. It may, therefore, be regarded 
as a convenient substitute, in certain cases, for the ordinary method ; 
and in this point of view alone I have been induced to submit it to 
your consideration. 
Lam, dear Sir, with much regard and esteem, 
Yours sincerely, 
Perth Academy, Nov. 2\, 1816. ADAM ANDERSON, 
ARTICLE V. 
Curjous Experiments on boiling Tar. By Richard Davenport, Esq. 
(fo Dr. Thomson.) 
DEAR SIR, 
Ir you think the following detail of a curious fact will be inte- 
resting to your readers, it is at your service. Some know, and 
many probably have heard without believing, and to others it will 
be quite new to liear, that a man can dip his hand into boilipg tar 
without suffering. I have met with gentlemen who had seen it 
done many years ago; but I never, till very lately, had an oppor- 
tunity of being myself an eye witness of the experiment ; and [ had 
supposed that the instances were not many, and that the escaping 
unhurt was owing to peculiar thickness, or to some other quality in 
the skin, or perhaps to some dexterous management, which either 
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