86o 



THE POPULAR SCIENCE MONTHLY 



had to be added to. It was then found that 

 the university had a much more valuable 

 collection than was at first supposed. 

 Among its most interesting and instructive 

 features were a typical lot of about forty 

 neolithic implements from Denmark ; stone 

 and pottery specimens illustrating the archfe- 

 ology of Michigan ; potsherds and pottery 

 vessels from the islands at the mouth of the 

 Amazon ; ancient Peruvian vessels from An- 

 con and Pacasmayo ; pottery vessels from 

 the East Indies ; skulls, including some of 

 the perforated crania described by Henry 

 Gillman, so mounted that they may be ex- 

 amined on all sides and measured without 

 handling; stone hammers or mauls from the 

 ancient copper pits at Isle Roy ale, Mich. ; 

 the De Pue collection of implements from 

 the surface of the immediate neighborhood 

 of the university ; and casts from the Smith- 

 sonian collections, with descriptions. Sev- 

 eral prehistoric village sites have been dis- 

 covered near Ann Arbor, which, it is hoped, 

 may soon be thoroughly examined. A sur- 

 vey has been made of one of the prehistoric 

 "garden beds" at Kalamazoo. As yet the 

 work of the museum has been chiefly con- 

 fined to archcBology, but it is expected that, 

 as the department develops, other phases of 

 anthropological science will be studied. 



The Conditions of Rain-making. The 



conditions of successful rain-making, as de- 

 fined by Prof. A. Macfarlane, of the Uni- 

 versity of Texas, in the light of Mr. John 

 Aitken's experiments on fogs and dust not 

 in a small portion of the atmosphere cut off 

 from the rest by means of an air-tight re- 

 ceiver, but on a large scale in the unbounded 

 atmosphere are : " If the air operated on is 

 at a temperature higher than its temperature 

 of saturation, it must be cooled down to that 

 temperature. Further, when the moisture 

 condenses it gives out latent heat, which 

 tends to arrest the process ; this latent heat 

 must be removed. It is not, as some rain- 

 makers have imagined, ' Pull a trigger ; Na- 

 ture will do the rest.' The only trigger- 

 pulling which experiments warrant as possi- 

 ble consists in supplying the necessary fine 

 dust for nuclei, so that condensation may 

 take place without delay when the air is 

 cooled to its temperature of saturation ; or 

 in supplying fine dust from such a substance 



as common salt, which has a chemical affin- 

 ity for water and may be able to accelerate 

 slightly the falling of a shower. Suppose 

 we take a cubic mile of the air upon which 

 Dyrenfurth operated on the night of Friday, 

 November 25, 1892. The record at the 

 weather office in San Antonio, at 8 p.m., gave 

 the temperature of the air as 72 Fahr., and 

 the dew point as 61 Fahr. To cool down 

 a cubic mile of that air to the dew point 

 would require the abstraction of as much 

 heat as would raise eighty thousand tons of 

 water from the freezing point to the boiling 

 point. To cool it do^vTi another eleven de- 

 grees would require as much more heat to 

 be abstracted. The amount of water set 

 free would be twenty thousand tons, which, 

 spread over a square mile, would give about 

 r4 pound per square foot, or toott of an 

 inch of rainfall. The amount of latent heat 

 set free by the condensation of that amount 

 of water would raise one hundred thousand 

 tons of water from the freezing point to the 

 boiling point ; and it would be necessary to 

 absorb this heat in order that the rain-mak- 

 ing might go on. I have supposed the cu- 

 bic mile of air to be kept constant ; if the 

 air operated on is constantly changing, the 

 task becomes one of infinitely greater diffi- 

 culty." It is hardly necessary to say that 

 Prof. Macfarlane considers the professional 

 rain-makers, the proceedings and pretensions 

 of eight of whom he reviews in his paper, as 

 "no better than the medicine men of the 

 Indians." 



inomalios in Weiglit. The anomalies in 

 weight at different points on the surface of 

 the earth, which have been recognized for a 

 considerable time, have been attributed to 

 corresponding anomalies in the figure of the 

 earth ; to the insufficiency of the formulas 

 for reduction to sea-level ; to the unequal 

 distribution of masses ; or to inexact obser- 

 vation. A study of the subject by the 

 French commander Defforges, which in- 

 cluded forty-one observations at twenty-five 

 stations of different latitudes and elevations, 

 shows that weight is distributed very un- 

 equally over the globe ; that Clairaut's law, 

 true as a whole, is nearly always marked by 

 notable anomalies ; that weight, on the shores 

 of different seas, presents feeble anomalies, 

 constant, and consequently characteristic, on 



