214 



SCIENCE. 



[Vol. XIX. No. 480 



ratio m : n can be expressed by smalljintegers the curve is com- 

 pletely shown by this apparatus. When this ratio cannot be 

 expressed by small, but can by moderate, whole numbers, the 

 curve cannot well be seen, but may be readily photographed. 

 The most beautiful effects are seen when the ratio m : n has 

 almost some such values as 1:1, 1:2, 2:3, or 3:1. The values 

 of a, &, and a vary with every tap of the finger, and thus 

 a single apparatus will show a great variety of curves of one 

 class. 



I have not tried projecting these curves with a lantern, but 

 I see no difficulty in the way of such a proceeding. 



Clark UnlTerslty. T. PROCTOE HaLL. 



VALUABLE EXPERIMENTS IN VEIN-FOEMATION. 



In No. 3, Vol. SIX., of the School of Mines Quarterly 

 there appeared a short paper " On the Genesis of Ore-De- 

 posits," by W. H. von Streeruwitz, the chief of the Western 

 Division of the State Geological Survey of Texas. 



In these days of hasty conclusions and the overcrowding 

 of scientific literature v?ith opinions and half -developed 

 theories, it is refreshing to run across an occasional example 

 of undue modesty in presenting the results of elaborate ex- 

 perimentation. My excuse for thus tardily calling attention 

 to a marked case of this character, entirely without the 

 knowledge of the author, is the conviction that the gentle- 

 man himself will not lay claim to full credit for the work 

 which he has planned and executed in a thoroughly scientific 

 manner. Especially does this action seem fitting as prelim- 

 inary to an extension of the same investigations by the 

 present writer iu the metallurgic laboratory of the Arizona 

 School of Mines. In fact, it is only just to confess that the 

 inspiration of these last experiments, for v?hich preparations 

 are now being made, came originally and wholly from the 

 most interesting results of Professor von Streeruwitz's patient 

 and intelligent observations in his laboratory at Houston, 

 Texas. 



In the paper quoted Professor von Streeruwitz does not 

 make very clear how much of the value of his well-fortified 

 conclusions rests upon the skill with which he has himself 

 conceived and executed a most convincing series of experi- 

 ments. But those who have seen some of the tubes with 

 miniature veins of gold, silver, copper, lead, etc., and others 

 with beautifully formed agates, need only the concise rea- 

 soning of the article referred to, in order to understand the 

 originality, perseverance, and devotion to truth with which 

 the investigation has been carried out through several years 

 of diligent experimentation. 



In the language of our author, the experiments would, so 

 far, appear to establish the following points, viz. : — 



1. It is principally the iron which, in silico-ferruginous 

 fissure veins, brought the other metals from greater to (by 

 mining) accessible depths. 



2. Most siliceous ore-leads, carrying also large quantities 

 of iron and having silico-ferruginous outcrops, seem to be 

 deposited from hot aqueous solutions of the metals and sili- 

 cates. 



3. Metals and metal combinations contained in the rock 

 surrounding the fissures and crevices were probably leached 

 out by the hot liquids contained in the fissures and precipi- 

 tated on and combined with the siliceous iron growing up in 

 the fissures. 



4. The fissures could be charged with ore-veins in a com- 

 paratively short time, since, no doubt, high temperature and 

 galvanic currents existed in the fissures at the time of forma- 

 tion of the ore-gangues. 



5. In contact-gangues the precipitation and deposition of 

 ores was materially facilitated by galvanic currents caused 

 by the contact of different rocks, and it is owing to the preva- 

 lence of galvanic currents that in most cases richer deposits 

 at the intersection of two or more leads were formed. 



6. The so-called iron out blows ("gossan," " eiserner hut," 

 "Pacos," "Colorados," etc.) are frequently not the product 

 of igneous eruption, but a deposition product from aqueous 

 solutions; and alterations in the rocks contiguous to such 

 outblows are not necessarily the result of eruptive agencies, 

 but of a leaching process. 



7. The formation of banded agates does not always take 

 place, as is generally believed, in the cavities of a rock, but 

 can also occur free in solutions; and the thickness of the 

 bands progresses from the centre outwards, although a re- 

 verse process by osmosis may be possible under certain con- 

 ditions. 



The bases for these conclusions are somewhat more explicit 

 than might, perhaps, be inferred from a reading of Professor 

 von Streeruwitz's paper alone, but, as he is most careful to 

 insist, the experiments possess their greatest scientific impor- 

 tance in the element of suggestiveness for future inquiry. 

 It is remarkable that so little has heretofore been done in 

 such directions; and, like the admirable flexure tests of the 

 United States Geological Survey in orographic work, they 

 point out little-trodden fields in geology which offer rich re- 

 wards to capable investigators who will approach the prob- 

 lems in inductive experimental mood, following the guidance 

 of results as they are gradually manifested. 



No one will be better pleased than Professor Streeruwitz 

 to know that others are earnestly engaged in this study. 

 The incidental discoveries, whatever they may be, are liable 

 to prove as interesting and valuable as any which may be 

 directly sought. Indeed, it is impossible at this juncture 

 to predict to what legitimate length the investigation may 

 lead. 



The main thing to be desired is the inauguration of a 

 large number of experiments with as widely varied condi- 

 tions as possible of material, situation, environment, and 

 activity. While co-operation is not really essential, it can 

 do no harm and may result most beneficially. May not 

 Sbme of our zealous young geologists be induced to undertake 

 this work, which should be continued with constant observa- 

 tion for a term of years ? 



Instruction will gladly be given to any who may require 

 it, and from those who cannot otherwise aid the cause 

 thoughtful suggestions will be most welcome. 



Theo. B. Comstock. 



Director School of Mines, Tucson, Arizona. 



ROYAL METEOROLOGICAL SOCIETY. 



At the meeting of this society on Wednesday evening, March 

 16, Dr. C. Theodore Williams, the president, delivered an address 

 on the "Value of Meteorological Instruments in the Selection of 

 Health Resorts." He drew attention to thermometers, maximum 

 and minimum, as the foundation-stone on which medical clima- 

 tology rests, and instanced effects of extreme cold or heat on the 

 human organism. The direct rays of the sun are of the greatest 

 importance, and in health resorts should be utilized to the full; in 

 fact, only climates where, during the winter months, even a deli- 

 cate person can lie or sit for several hours a day basking in the 

 sunshine are to be recommended for most complaints, and the 

 various forms of sunshine recorders are used to aid the medical 

 adviser in choice of such health stations. 



After referring to the value of rain-gauges, hygrometers, and 

 barometers, Dr. Williams stated that many health resorts owe 

 their reputation almost solely to their shelter from cold winds; for 



