October 30, 1891.J 



SCIENCE. 



249 



stitution of the Qiatter absorbed being different from what it was 

 before its solution, leaves no doubt that that process is molecular 

 also: the oxygen and nitrogen molecules, whose intermixture, 

 through diffusion, constitute the atmosphere, are disassociated, 

 the water taking into solution a much larger proportion of the 

 oxygen. This could not possibly occur if the process of solution 

 were not molecular. If the air is composed of the molecules of 

 oxygen and molecules of nitrogen so intermixed as to constitute a 

 continuous substance, a process which takes more of the oxygen 

 than it does of the nitrogen is necessarily molecular. 



It seems, therefore, that we are authorized to conclude not only 

 that the waves themselves are the result of motion of the mole- 

 cules constituting the water, and not of masses of such molecules, 

 l)ut that when wind causes the waves, its friction, in part if not 

 entirely, is due to the passage of molecules from one fluid into the 

 other. Daniel S. Trot. 



Montgomery, Ala , Oct. 23. 



Rain-Making. 



As Professor Hazen. in his letter published in Science of Oct. 

 16, garbles the quotation from Plutarch which is relied on to 

 prove that the ancients had the same notion in regard to rains 

 following battles that prevails at the present time, I beg leave to 

 give the passage entire, for it is only by a consideration of the 

 whole that his meaning can be arrived at. Plutarch says, in his 

 life of Marius, speaking of the defeat of the Ambrones by the Ro- 

 mans: 



' The Romans pursuing, either killed or took prisoners above a 

 hundred thousand. Other historians give a different account of 

 the number of the slain. From these writers we learn that the 

 Massilians walled in their vineyards with the bones they found in 

 the field, and that the rain which fell the winter following, soak- 

 ing in the moisture of the putrefied bodies, the ground was so en- 

 riched by it that it produced the next season a prodigious crop. 

 It is to be observed, indeed, that extraordinary rains generally 

 follow after great battles; whether it be that some deity chooses 

 to wash and purify the earth with water from above, or whether 

 the blood and corruption, by the moist and heavy vapors they 

 'emit, thicken the air, which is liable to be altered by the smallest 

 cause." 



Now, if we take by itself the statement that "extraordinary 

 rains generally follow after great battles," it would appear, indeed, 

 that the ancient ideas on this subject were identical with those 

 prevailing in modern times. But if we ask the question, ' ' How 

 long after the battles did the rains occur to which Plutarch al- 

 luded '!" and look for our answer in the context, we shall see, as I 

 said in my letter in Science of Oct. 7, that the notions of the for- 

 mer on the subject appear to have been wholly different from 

 those of the latter. When did the rains follow the battle between 

 the Ambrones and the Romans ? In the winter following. When 

 did rains follow any other battles that Plutarch had in mind, or 

 when did he think they followed? After the bodies of the dead 

 had putrefied. How soon could the "blood and corruption" — 

 especially the corruption — emit "moist and heavy vapors?" 

 Not under a week. How soon could " some deity wash and pu- 

 rify the earth with water from above?" Not under several 

 months. 



It matters not how erroneous Plutarch's ideas were as to why 

 rains followed after battles. It is not his conclusions with which 

 we have to deal, but we are trying to find out what he supposed 

 the facts to be on which he based them. In doing this we have 

 no right to assume as facts anything that is inconsistent with his 

 view of the case. 



Professor Hazen quotes the opinion of another rain-maker in 

 opposition to my own. He might also have quoted me against 

 myself. In an article written by me and published in the Golden 

 Age of May 11, 1872, and which is also copied into the appendix 

 to the revised edition of " War and the Weather," occurs the 

 following passage: 



" If great noises cause rain, some other less expensive way may 

 be devised to produce them. It was noticed, even in ancient 

 times, that great rains followed battles, and it is not impossible 



that the shouts of a great multitude, with the clashing of metal 

 on metal, may produce the same effect upon the air as the firing 

 of cannon. Should all the inhabitants of a city at a given hour 

 unite in creating an uproar with hands and voices, it would seem 

 to one in our day as though the world were returning to barbar- 

 ism; but in the higher civilization of some age to come, this may 

 perhaps be a common occurrence." 



The other rain-maker refen-ed to has evidently adopted this 

 idea without having made any more critical examination of the 

 passage quoted from Plutarch than I had done when the above 

 was written. But though I have changed my mind in regard to 

 the meaning of this passage, it would be going too far to say that 

 ancient battles did not immediately produce rain, and that the 

 above does not furnish the true explanation of the phenomenon. 

 I only afiSrm that Plutarch did not say that rains immediately 

 followed great battles, and that the inference that he thought they 

 did cannot be drawn from what he does say. I contend further 

 that, even if the ancients thought that battles produced rain, they 

 may have been wrong, while the moderns may be right in that 

 opinion. Coincidences sometimes occur in thought as well as in 

 action and events. 



In speaking of the battles of the late war, and their supposed 

 effect upon the atmosphere, Professor Hazen says, "Mr. Powers 

 thinks that the currents of the atmosphere do not travel at the 

 rate of twenty to fifty miles per hour, or, at least, during these 

 battles they did not do so." This is hardly a fair statement of 

 my position. I think it very probable that portions of two cur- 

 rents moving in nearly opposite directions, in mingling together, 

 lose to a great extent their original motion, and take on a circular 

 motion, moving for a time neither very far east nor very far 

 west. I think that in this way the influence of the concussions 

 may I'emain in the vicinity of the firing until enough air of dif- 

 ferent temperatures has mixed together to develop a rain-storm, 

 and that then the storm will move eastward along with the cur- 

 rent that supplies the greater portion of the moisture that forms 

 the rain. 



Professor Hazen repeats his statement that "one thing seems 

 very certain, that absolutely no rain can be obtained out of a dry 

 atmosphere," and eliminates from it the word " seems." It is not 

 apparent how this helps it as an argument against the artificial- 

 rain theory. According to my understanding of his first article, 

 he did not state this as an abstract idea, but in order to show how 

 unreasonable it was, in his view, to expect to produce rain by 

 concussion in certain states of the atmosphere ; and by ' ' atmos- 

 phere " I naturally understood him to mean the same thing that 

 he would mean if he were speaking of measuring the humidity of 

 the atmosphere with his instruments. My contention is that there 

 is nothing unreasonable in expecting to produce rain, however 

 dry such air may be, for we are constantly receiving, by the ve- 

 hicle of air-currents, supplies of aqueous vapor from the tropical 

 portion of the Pacific Ocean; and these currents and the vapor 

 they bring occupy a high altitude, and there the clouds and rain 

 are formed. 



Professor Hazen says, " It certainly is not a fact that two cur- 

 rents pass in opposite directions near the point of formation of 

 our storms." How does he know this ? He must admit that 

 there is a current moving constantly from west to east or from 

 south-west to north-east. How does he know what there is above 

 this current ? Professor Maury gives very strong reasons for be- 

 lieving that there is a polar current there flowing in nearly the 

 opposite direction. Has any one ever given as good reasons for 

 believing to the contrary? Professor Maury's theory was not 

 evolved from a few isolated facts, but from a comprehensive 

 knowledge of the winds throughout the whole world, or so much 

 of it as could be reached by navigators. Has his theory of the 

 circulation of the atmosphere ever been overturned, or even seri- 

 ously attacked ? When I speak of air-currents, one bringing 

 tropical moisture and the other polar cold, I am not drawing 

 upon my own imagination for props to support the theory of arti- 

 ficial rain production, but I am availing myself of the result of 

 investigations and deductions by one who, as a man of science 

 was a peer to any whom this country has ever produced. 



Delavan, Wis., Oct. 19. EDWARD POWERS. 



