August 11, 1922] 



SCIENCE 



169 



of a citron color. On some plants the petals 

 are more or less laciniate on the margin. Fre- 

 quentlj' they are five in number, sometimes six, 

 often eight. The number of pistils is not fixed, 

 and the bifid cotyledon and broad rim of the 

 torus, both traits normally characterizing the 

 true calif ornica (the smooth perennial), are 

 often as elusive as the other characters. 



The color especially lends itself to modifica- 

 tion by selection. Burbank once found a plant 

 with a crimson streak like a red thread at the 

 base of each petal. Saving the seed, he ob- 

 tained through selection alone a poppy with 

 the flowers all crimson. Seedlings from Bur- 

 bank sometimes have pinkish flowers, almost 

 white. 



Eschscholtzia has certain advantages over the 

 evening primrose for experimental purposes. 

 It is a natural species oceuiiing by the million 

 in its habitat. Though very difficult to trans- 

 plant, it gi'ows readily from the seed. It is 

 therefore not a garden variant, nor a suspected 

 hybrid. (Enothera lamarckiana, thus far the 

 subject of most mutation experiments, though 

 cultivated in Eui-ope, is American in origin. 

 No one, I believe, has yet ever found it growing 

 wild anywhere. 



In any event, accurate studies of the varia- 

 tion in Eschsclioltzia should be interesting and 

 repaying. 



David Stake Jordan. 



THE TEMPERATURES OF METEORITES 



In the last number of Science'^ Dr. Gfeorge 

 P. Merrill discusses some matters connected 

 with meteorites. With regard to their tem- 

 perature he says, "it seems certain that they 

 have been wandering for an indefinite period 

 in space and at a temperature of 'absolute 

 zero.' At the time of entering our atmosphere 

 it is fair to assume that they are cold through- 

 out to a degree of which we can have no con- 

 ception." It has seemed to me worth while to 

 examine roughly what temperature a meteorite 

 might reasonably be expected to have just be- 

 fore it enters the atmosphere of the earth. The 

 meteorite has certainly been for some time ex- 



1 Science, 55, p. 675, 1922. 



posed to radiation from the sun, and it may 

 well be that its temperature is much higher 

 than the absolute zero. 



To get some idea as to the temperature sup- 

 pose that the meteorite is a sphere with a black 

 surface, and that the material of which it is 

 composed is a perfect conductor of heat. The 

 temperature of this sphere is determined by 

 the condition that the rate at which it loses 

 heat by radiation equals the rate at which it 

 receives heat from the sun. The condition is 

 expressed by the equation 



47tr=aO* = %r-b-^, (1) 



where r stands for the radius of the meteorite, 

 o for the constant in the Stefan-Boltzmann 

 radiation formula, 6 for the absolute tempera- 

 ture of the meteorite, b for the solar constant, 

 and e and d for the respective distances of the 

 earth and the meteorite from the sun. If we 

 take 17 as 1.279-10-1= cal./cm^.sec.deg.* and b 

 as 1.93 cal./em=.min. (1) leads to 



9 - 282>Jj (2) 



Thus if black spheres which conduct heat per- 

 fectly were placed at the same distances from 

 the sun as the several planets, (2) shows that 

 the temperatures of these spheres would be the 

 following : 



At the distance of 



Mercury igO" C. 



Venus 58° C. 



Earth 9= c. 



Mars — 45° C. 



Jupiter —149° C. 



Saturn — 182° C. 



Uranus — 209° C. 



Neptune — 221° C. 



We see that in the neighborhood of the earth 

 such a sphere would have a temperature above 

 that of melting ice! 



But a meteorite is not a perfect conductor 

 of heat. Suppose we apply the above method 

 of reasoning to a sphere which is a perfect 

 non-conductor of heat, covered, except along a 

 narrow equatorial line, by a thin layer of a 

 substance which is a perfect conductor of heat 

 and is black. The conducting layer forms two 

 separate caps, and if one cap is turned toward 

 the sun and the other away from the sun we 



