W. J. McGee—Secular Climatal Changes. ‘7 
Art. LVII.—A Contribution to Croll’s Theory of Secular Oli- 
matal Changes ;* by W. J. McGun, of Farley, Iowa. 
BRIEFLY stated, Dr. Croll’s theory of secular changes in ter- 
restrial climate indicates that during periods of high eccentricity 
in the earth’s orbit the hemisphere whose winters occur 
aphelion suffers, through the intervention of physical and me- 
teorological agencies, a diminution of temperature, while on the 
opposite hemisphere the temperature is correspondingly aug- 
mented.t It is the object of the present communication to 
direct attention to certain meteorological relations tending to 
produce such an effect, which appear to have been heretofore 
overlooked. 
All extensive series of meteorological observations which 
have been examined by the writer indicate the existence of a 
general law, which may be expressed by the proposition: Any 
increase in annual or diurnal thermometrical range is accompanied 
by a diminution in mean temperature. Aside from the colloca- 
tion of a portion of the results of an Salita meteorological 
survey, for the purpose of establishing an empirical coefficient 
indicating the efficiency of the law in absolute measure, no 
discussion of this proposition will be here offered. 
The accompanying table I is based upon Charte III of W. 
H. Dove’s “Verbreitung der Wirme auf der Oberfliiche der 
Erde,”§ and exhibits temperatures along the meridians passing 
through, = Atlantic Ocean (long. 20° W.) and Central Asia 
(long. 120° E.). 
TABLE I, 
Temperatures at 20° W. and 120° E. of Greenwich. 
Long. 20° W. Long. 120° E. 
Latitude 
January. July. Range, January. July. Range. 
0° + 79°2° + 770° a 22 LITO +81°5° 4°5° 
20 70 TT0 7:0 60°6 81°5 20°9 
40 5 68-0 et 264 154 49-0 
60 36°0 67°2 21°2 —34:0 63°5 975 
Polar circle 26:2 45°65 19°2 40°0 6071 100°1 
__ Mean 68°4 73°3 4°9 53-4 78°8 25°4 
* Read before thie —_— Academy of re sary: J om gh 1880, and agg in 
brief abstract in the oceedings, vol. i, pt. 1, p. 2 d before meri- 
ean Association for the “Advecieeniaat of ANeats at ial Angst ott 1881. 
n inb, and Dublin Phil. Mag., Aug., 1864, Feb., 1867, “ Climate 
and Time,” Edinburgh and ab York, 187: 
¢ Cf. Proceedings Ameri: n Association, vol, xxix, Boston Meeting, 1880, 
p- 486, et seq. § Bartis, 
