180 



SCIENCE 



[N. S. Vol. XXXIX. No. 



to see to what extent the pharmacognosist and 

 pharmaceutical chemists have contributed to 

 make the mierochemistry of plants an impor- 

 tant branch of phytochemical investigation, 

 pure as well as applied. 



It ought to be possible in the future to sup- 

 plement the maerochemical investigation of 

 plants in a manner that should prove produc- 

 tive of the very best results. If the micro- 

 scope, supplemented by accessories and chem- 

 ical reagents, is going to enable the phyto- 

 chemist of the future to extend the macro- 

 scopic examination carried out on one or sev- 

 eral species to all members of a genus or even 

 family with a minimum of material and pos- 

 sibly of time, the boundaries of plant chemis- 

 try ought to be extended farther in a decade 

 than they have been during a century. 



E. K. 



THE ORIGIN OF CLIMATIC CHANGE Si 

 The discussion of meteorological observa- 

 tions shows clearly that climates undergo va- 

 riations of short duration, but such records as 

 the presence of old lake beaches and the exist- 

 ence of well-marked glacial moraines, and 

 other geological evidence distinctly point to 

 climate changes covering long intervals of 

 time. The evidence is not sufficient to char- 

 acterize the variations as periodic, but the ice 

 ages are sufficient to point to times when the 

 conditions reached were extreme. 



What may reasonably be assumed to be the 

 chief established facts about such extensive 

 changes may be summed up briefly as follows : 

 Climatic changes were several, and probably 

 many. Similar simultaneous changes oc- 

 curred over the whole earth, or, in other words, 

 it was warmer or colder over the whole earth 

 simultaneously. These times of warmth or 

 coldness were unequal in intensity and dura- 

 tion, and of irregular occurrence, and, lastly, 

 they have taken place from very early, if not 

 from the earliest geological age down to the 

 present. Numerous theories, both probable 

 and improbable, have been suggested from 

 time to time to account for the origin of such 



1 From Nature. 



world-wide changes, and while each has its ad- 

 vocates, perhaps only three may be said to 

 claim attention to-day. These may be briefly 

 stated as the eccentricity theory (Croll), de- 

 pending on the eccentricity of the earth's 

 orbit; the carbon dioxide theory (TyndaU), 

 based on the selective absorption and variation 

 in amount of carbon dioxide; and thirdly, the 

 solar variation theory, on the assumption of 

 solar changes of long duration. A new theory, 

 which may be called " the volcanic dust and 

 solar variation theory," has recently been put 

 forward by Professor W. J. Humphreys,^ 

 under the guarded heading, " Volcanic Dust 

 and Other Factors in the Production of Cli- 

 matic Changes, and Their Possible Eelation 

 to Ice Ages." 



The author carefully points out that the 

 idea that volcanic dust may be an important 

 factor in the production of climatic changes is 

 not new, but " though just how it can be so 

 apparently has not been explained, nor has the 

 idea been specifically supported by direct ob- 

 servation." He remarks also that while the 

 pioneers regarded the presence of volcanic 

 dust in the atmosphere as an absorbent of 

 radiation, and so lowered the earth's tempera- 

 ture, modern observation suggests the oppo- 

 site effect, namely, the warming of the earth's 

 surface. 



In putting forward his views of the action 

 of dust. Professor Humphreys proceeds first 

 to indicate that the dust that is effective is that 

 which is situated in the atmosphere in the iso- 

 thermal region or stratosphere. He then 

 enters into the question of the size of the par- 

 ticles and probable time of fall, and concludes 

 that particles of the size of 1.85 microns in 

 diameter would take from one to three years to 

 get back to the earth if they originally had 

 been thrown up by a volcanic eruption. 



Considering next the action of the finest and 

 therefore most persistent dust on solar radia- 

 tion, he finds that the " interception of out- 

 going radiation is wholly negligible in com- 



2 Journal of the Franhlin Institute, August, 

 1913, Vol. OLXXVI., No. 2, p. 131; also Bulletin 

 of the Mount Weather Observatory, August, 1913, 

 Vol. VI., Part 1, p. 1. 



