476 



METEOROLOGY. 



reduced to tlio freezing point would Le 30 — 0.090 + 29.910 standard inches, 

 761.75 — 2.0/i = 759.70 standard mm, a result wliicli corresponds with the 

 figures of the tables. 



For particular purposes the case may be put briefly as follows : At the 

 respective standard tem}wraturcs 1 inch = 25.39954""" or 25.4"""^ nearly. At 

 62° F., and therefore at any other temperature common to the two scales, 1 inch 

 = 25.4 (1 — 30(r)™'", where a equals the coefficient of dilatation of brass for 1° 

 F. = 0.0000104344, 1 inch = 25.4™°^ — 0.008 = 25.392°^°^. Therefore, at 

 the standard temperatures 30 inches = 25.4'"'" x 30 = 762"™ as in the tables. 

 At a common temjyeratiire 30 inches = 762.0'"™ — 0.008 X 30 = 761.760™™. In 

 practice this is sufficiently near, but if greater accuracy be required, the follow- 

 ing figures may be ado])ted as the respective equivalents of an inch and a milli- 

 metre at all common temperatures : 1 inch = 25.3916™™ and 1™™ = 0.0393831 

 inches. The following tables are constructed on this basis : 



TABLE L 



The tables to which I have throughout refeiTcd are those published by the 

 Smithsonian Institution, Washington, among their Miscellaneous Collections 

 and under the able editorship of Professor A. Guyot. (Second edition, Wash- 

 ington, 1858.) 



F. F. TUCIvETT. 



APPENDIX B. 



The common method of calculating the annual means of the temperature and 

 atmospheric pressure from the monthly means is not quite exact. I presented a 

 paper on this subject to the Silesian Society for the Progress of the Country, 

 ('• Schlesische Gesellschaft fur vaterlandiscli'e Kultur,") of which I beg leave to 

 give here an abstract. 



The monthly means being the quotient of the sum of the daily means by the 

 number of days in the month, it is clear that we o1)tain that sum by multiplying 

 the given monthly mean by the corresponding number of days. This being- 

 done with all the 'months composing the yeai-, "the sum of these twelve products 

 will be equal to the total sum of all the daily means in the year, which divided 

 by 365 (or by 366 in a leap year) gives the true annual mean. The ditierence 

 of the true mean and the common mean increases with the divergencies of the 

 monthly means. 



Tlie ordinary mean temperature of Caracas ^\•ould be, taking the numbers 

 given in the foregoing table, 71°.707, while the true mean is 71°^711 ; the ordi- 



