80 PROFESSOR FORBES’ INQUIRIES 
gression of temperature under the 50th and 60th parallels. The numbers for 80° 
and 90°, and in a great measure also that for 75°, rest upon a method of graphical 
interpolation, explained by M. Doveat p. 13 of his Distribution of Heat, &c., which 
I have verified ; but it must of course be received with considerable allowance. 
The formula is least accurate about latitude 30°, evidently depending on certain 
physical peculiarities which cannot be embraced in so simple an expression.* 
21. The numbers in the second column of Table I. are projected in Plate II. 
§ IL. The Distribution of Land and Water according to Latitude on the Globe. 
22. It has been stated in the introduction to. this paper that the unequal distri- 
bution of land and water on the surface of the globe is the leading cause of the 
irregular distribution of temperature, considered independently of the latitude ; in 
other words, of the Thermic Anomaly. If we are to trace the connection between 
the temperature of a given parallel and the amount of land on that parallel, it 
will be convenient to form a table of this amount for every 10° of latitude, both 
north and south, compared to the entire circumference of the parallel. This is 
as perpendiculars erected on a straight line at intervals corresponding to the latitudes at which they 
intersect the given meridian. An interpolating curve being drawn easily among the extremities of 
these perpendiculars, the abscisse corresponding to every 5° of latitude are ascertained and tabulated. 
The mean of these numbers, taken round the whole circumference, gives the required number for each 
parallel. I think it worth while to preserve the numbers I have obtained, which are given in the 
following table, as they may be of service in future inquiries. I may here add, that the character 
of the climatic gradation in different latitudes is highly instructive. The curves of temperature cor- 
responding to oceanic meridians, such as that of Greenwich, are everywhere decidedly concave to the 
axis (representing a variation depending nearly on the simple cosine), while those of the continents, 
such as longitude 120° E., tend to become convex towards the axis in the higher latitudes (inclin- 
ing to the law of the (cosine)”), or else they form almost a straight line sloping towards the pole. 
This is in conformity with what has already been said in par. 4. See also par. 28 below. 
TaBLE of TEMPERATURES (FAHRENHEIT) deduced from M. Dovz’s Potar Cuart of 1857. 
LonGITUDE East OF GREENWICH. 
Latitude|); ye DT ane 
North. Mean. 
0° 20° | 40° | 60° | 80° | 100° | 120° | 140° | 160° | 180° | 200° | 220° | 240° | 260° | 280° | 300° | 320° | 340° 




50° |]58° |47° |44° | 419-5) 389° | 36° |383°5)37° |41° |42°:5) 47° | 51° | 48° | 88° | 383° |384°%5) 44° | 54°-5|| 425 







60 |/45 5/40 | 386 -5)31 -5) 27-5) 25 120 |22-5)28 |25:°5)27 |386 |29°5)21 |17 | 24-5) 34-5) 42-5) 29 -8 

65 40 |86°5)88 (26 |23 |19-5)138 |18-5}20 {18 |19 |20 {17 |11 {11 |22 | 29-5) 34-5) 22-6 


70 1/83 -5/383 |29-5)22 |20 |15 6:5) 6°5)12 |12 -5) 11-5) 10 5 2°5| 8 |16°5)24 | 27-5) 16-4 





75 ||26 |28 |24 |18-5)16°5)10 | 1 0°5) 5 6-5) 5:5} 3°5)—5 |—1 | 5 |10-5)18 | 21 || 10: 75 





* The great simplicity of the formula (par. 18) turns upon the accidental circumstance of the 
zero of FAHRENHEIT’S scale so nearly coinciding with the temperature of the pole, as Sir D. BrewsTER 
long ago remarked. The formula would represent the numbers of M. Dovz slightly better if a small 
constant term were introduced ; thus, T=1°+ 80° cos? (A—6° 30’), and in using any other thermo- 
metric scale this might be preferred. This formula becomes 
T= —17°2+44°4 cos? (A—6° 30’) on the Centigrade scale. 
T= —13°8 + 35°5 cos? (A—6° 30’) on Reaumun’s scale. 
