A LAST WORD. 
273 
hours eight P.M., four A.M., and noon ; the variation of the com- 
pass occasionally ; and the set of the current whenever encounter- 
ed. These observations, to be worth having, must be accurately 
made ; and as every thermometer and every barometer has its 
sources of error, consequently, every ship-master who undertakes 
hereafter to co-operate with us, and keep an abstract log, should 
have his barometer and thermometer accurately compared with 
standard instruments, the errors of which have been accurately 
determined. 
These errors the master should enter in the log; the instru- 
ments should be numbered,, and he should so keep the log as to 
show what instrument is in use. For instance, a master goes to 
sea with thermometers Nos. 4719, 1, 12, &c., their errors having 
been ascertained and entered on the blank page for the purpose 
in the abstract log. He first uses No. 12. Let it be so stated in 
the column of Remarks, when the first observation is recorded, 
thus : Thermometer No. 12. During the voyage. No. 12 gets bro- 
ken, or for some reason is laid aside, and another, say 4719, is 
brought into use. So state when the first observation with it is 
recorded, and quote in the column of Remarks the errors both of 
Nos. 12 and 4719. Now, with such a statement of errors given in 
the log for each of the instruments, according to the number, the 
observations may be properly corrected when they come up here 
for discussion. 
It is rare to find a barometer or a thermometer that has no er- 
ror, as it is to find a chronometer without error. A good ther- 
mometer, the error of which the maker should guarantee not to 
exceed in any part of the scale one degree, will cost, in the United 
States, not less than $2, perhaps $2 50. 
The errors of thermometers sometimes are owing to inequali- 
ties in the bore of the tube, sometimes to errors of division on the 
scale, &c. Therefore, in comparing thermometers with a stand- 
ard, they should be compared, at least, for every degree between 
melting ice and blood heat. 
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