90 
As those who can not make use of the actinometric degrees deduced 
by Marié-Davy from his observations of his conjugate bulbs will 
necessarily have to use either the simple observations of clear sky 
and cloudy sky, as given by the sunshine recorder, or the equivalent 
personal observations of the clouds, I give the following tables, which 
show how nearly parallel these two phenomena may be. Evidently 
in our study of the influence of insolation on crops in America from 
year to year we may use the sunshine recorder or the ratio between 
the actual and the maximum possible duration of sunshine without 
much error, at least in the growing season. 
Mean of five daily actinometric observations at Montsouris, expressed in Maric- 
Davy’s actinometric degrees or percentages of maximum possible intensity. 
| | | | 
Month. | 1875. | 1876. | 1877. | 1878. | 1879. | 1880. | 1881. 1882. | 1883. | 1884. | 1885. 
= wt pues Bl SS Say a eve | scabised| Sere es 
| | | a 
(Mprile see 2 11T EA | 44.1} 40.1] 36.3] 35.4] 28.6} 38.9] 33.0] 39.7] 868) 845] 341 
Maryse! Hsee footed 7.7) 45.8) 38.7) 41.5) 40.6) 50.3] 48.9] 47.4) 45.9] 46.3) 40.3 
une ee see ee ae 46.0 | 48.8) 54.5] 47.7] 45.1] 41.2] 533] 47.0] 45.3] 43.2] 46.1 
Taly pene eke 47.3} 521] 48.6] 50.6] 41.2] 50.0| 52.0] 46.6| 422] 43.4] 49.4 
Auguste: arate 39.9 42.0| 43.2] 87.8] 42.3) 30.1] 40.3] 34.0] 39.0] 36.2] 36.4 
September. _-....-_.- | 95.7 | 30.9] 31.4] 30:9] 82.7] 30.2] 28.3) 27.1 | 30.5) 308) 20a 
me eS | | 
Average ------- 43.5 | 43.5) 42.1] 40.7 | 38.0) 41.6) 42.7 |) 40.3/ 39.9) 30.1) 38.4 
| 
Mean of five daily observations of the cloudiness at Montsouris expressed as ratio 
of the actual duration of sunshine to the maximum possible duration. 
Month. | 1875. | 1876. | 1877. | 1878. | 1879. | 1880. | 1881. | 1882. | 1883. | 1884. | 1885 
| | | 
Pari oot ee ge 2 | 0.66) 0.60] 0.54] 0.53} 0.43] 0.58] 0.49| 0.60] 0.55] 0.52] 0.51 
Mayes ae er Ne 6441 68:] =2ee'l< S86 > 555] 568° 266 |i 64 [see 62: mene? D4 
Tne tees ser eae a .60| .64] .71| .62| .59| 154] .70| 61] .59 56 60 
Til y eee ee GSE oe .63| .69| 64] .67| .55| .66| .69 62} .56] .57 BD 
Paste ees | .57| .60] .62 54/ .61| .56] .58| .50| .56] .52 52 
September.---------- . 62 54 OD 54 67 .53 49 AT 53 54 42 
Average -.-..-- | .e2| .62| .60| .58| .55] .59| .60| .57| .67| .55| 52 
RELATIVE TOTAL HEAT RECEIVED FROM SUN AND SKY 
DURING ANY DAY, BY HORIZONTAL SURFACES. 
A more accurate way of considering the amount of insolation at 
any locality is to compute the total radiation (expressed by its equiva- 
lent heat in calories) received by a horizontal surface in the natural 
daytime of that day and latitude, taking account of the absorption by 
the atmosphere. (See Annales Agronomique, 1878, IV, pp. 270-296, 
or Ann. Report Chief Signal Officer for 1881, pp. 1200-1216.) This 
has been done by Aymonnet by a graphic method. He assumes that 
if the sun were in the zenith then the unit of horizontal earth’s sur- 
face would, because of atmospheric absorption, receive only 0.75 of 
