1880.] o iiia 737 
fore I have restricted the above table to that range of temperature 
within which we have satisfactory observations, and which corres- 
ponds most nearly to what generally occurs in practice. 
The above table may also be put in the general algebraic form: 
In hours H = 1560 — 12 (T — 50°) 
In days D = 65 — % (T — 50°) 
where T represents the average temperature to which the eggs 
are exposed. We see from this that the heat received by the eggs 
while resting for sixty-five days in a light, dry, sandy soil at a 
uniform temperature of 50° F. is the least that will hatch them, 
while the additional term 14 (T—s0°) represents the acceleration 
of the process consequent upon maintaining a higher tem- 
perature. 
Ll. The Temperature experienced by the Eggs in the Ground—In 
order to apply the results of the preceding section we must know 
the temperature of the ground in which the eggs are deposited, 
that is to say especially the duration of such temperatures as are 
above 50° F. 
Actual observations of the soil at depths of one-half, one, one 
and a-half, two inches, &c., are, so far as I know, sadly lacking in 
this country, and rarely to be found in Europe, although very 
much needed in. special investigations. An exhaustive review of 
our knowledge on the subject of earth temperatures has been 
published, during the past year, by Wild, of St. Petersburg, but 
it is concerned mostly with temperatures at greater depths than 
six inches, and relates, therefore, to terrestrial physics rather than 
to agricultural interests. 
In the absence of direct observations, I have therefore adopted 
as a working hypothesis some empirical approximate relations 
between the air temperatures (published in the annual report o 
the Chief Signal Officer, Gen. A. J. Myer) and soil temperatures 
at the depth of one-half inch, from which I have deduced the 
following table showing for each station the total number of hours 
in each month during which the eggs must have been exposed to 
temperatures of over 50° and reduced to an equivalent of 60°. 
Manik Fort Garry.| Breckenridge.| Yankton. | North Platte. | Dodge City.| Corsicana. 
~ | He 
T Lat, 50° Lat. 46.5° | Lat. 42.5° | Lat. 41.5° | Lat. 37-5° | Lat. 32.09 
1875. 5 A E | : ; x 
DY ay ge 8 496 538 620 
in oer ta 372 | ie 372 496 Fo 3s 744 
O Ptember 324 406 4 540 6 
October A ETEEN 48 180 275 3 48 540 
November.. | o 36 72 264 464 
December pise o o 28 6o 144 372 
1876. 
pra i o o 20 20 120 324 
ebruary ‘a s Sá 64 180 324 
BEER ea o o ' o 54 104 46 
April ROAR ae 66 78 18 : 276 324 600 
May . eee 324 290 3 464 558 ; 744 
de aao. 594 420 480 S 690 920 
eee atte 
ena 
