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 w^hen 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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