500 



SCIENTIFIC RECORD FOR 1883. 



observations of sea and air temperatures as given in the first three col- 

 umns of the following table : 



Observations on board H. M. S. Challenger, 1873-1876. 



Hoar. 



Departures from daily means of observations taken every 

 two hoars. 



2a.m... 



4 a. m . . . 



6a.m... 

 8 a.m... 

 10 a. m . . . 



Noon 



2 p. m... 



4 p.m... 



6p. m... 



8 p.m... 

 10 p.m... 

 Midnight 



Temperatures. 



126 days in mid- 

 ocean. 



Air. 



Sea- 

 water. 



O J\ 



—1.13 



1.40 



1.41 

 —0.21 

 +0.78 



1.45 



1.80 

 1.56 

 +0.73 

 —0.30 

 —0.80 

 —1.02 



O J7>. 



—0.24 

 .33 



.29 



— .12 

 + .06 



.24 



.47 



.47 



.26 



+ .02 



— .19 



— .35 



76 days 

 near land 



Elastic force of 

 vapor. 



Air. 



-SI 



g = o 



•SJi 



o ]?. 



C Min. \ 

 \— 2.05J 



Inch. 

 — 0. 015 



020 



016 



007 

 + .004 



{£&} + •<>" 



+ .020 

 + .017 

 + .007 

 + .002 

 — .005 

 + .003 



^5 ts i © ."ti ^ oo 



" 9 «8 



Inch. 

 -0. 003 



.010 

 .003 

 .014 



.007 

 .015 

 000 

 .004 

 .005 

 .007 



11 r. I* , 



■HIS 



.a .oo 



Perff. 



+2 



+2 



+1 







—1 



—3 



—2 

 — 1 

 

 + 1 

 +2 



U C d; 



O CD' 



p P-w 





Inch. 

 —0.012 



— .022 



+ .003 

 + .028 

 + .032 



f .006 



— .043 



— .055 



— .028 

 + .004 

 + .013 

 + .012 



Force of wind. 



Open sea, f™[ 

 650 days. LJ"^ 



Pr. ct. 

 59 



50 



62 

 62 



58 



Thus the amplitude of the daily fluctuations of the air is 3.21, or 

 nearly four times greater than that of the surface of the sea below it. 



Near the land on 76 days the daily range of air temperature was 

 still larger. Part but not all of the observed greater range of air over 

 the sea surface is doubtless owing to the effect of heating the vessel's 

 deck, but the general fact remains as one of considerable interest. The 

 diurnal variations at sea of elastic force of vapor and of relative hu- 

 midity are shown by the fifth and sixth columns of the table drawn 

 from the Challenger observations. The disturbance induced by prox- 

 imity to laud is very notable. The land breeze delays the minimum va- 

 por tension two hours, i. e., from 4 to 6 A. m., and the sea breeze pro- 

 duces a secondary minimum, -f 0.007 at 2 p.m.; similar minima occur 

 at Batavia and at Bombay, apparently owing to the same cause, namely, 

 the mixing of descending dry air with the moist sea breeze. The diur- 

 nal variation at sea of relative humidity is given in the seventh column 

 and that of barometric pressure in the 8th ; the latter evidently repre- 

 sents only a small portion of the whole series of observations at his com- 

 mand; these however are quoted by Buchan principally as illustrating 

 his explanation of the origin of the diurnal period in pressure. On this 

 interesting though comparatively unimportant subject, Buchan has made 

 a most extensive study, parte of which have been published some years 

 ago, both inthearticle " Atmosphere" and inhis memoir in theEdinburgh 



