64 REPORT — 1901. 



In turbid solutions of gum mastic, soap, or oleic acid one may see 

 these air bubbles. In turbid solutions of kaoline or silica they act as a 

 Cartesian diver ; the suspended particles and the layers of particles rise 

 if they are lighted up by sunshine and sink again in shadow by a change 

 of density or volume of the air. 



V ndergrotmd Temperature. — Tiventif-second Report of the Committee, 

 consisting of Professor J. D. EvERETT (Chairmmi and Secretary), 

 Lord Kelvin, Sir Archibald Geikie, Mr. James Glaisher, Pro- 

 fessor Edward Hull, Dr. 0. Le Neve Foster, Professor A. S. 

 Herschel, Professor G. A. Lebour, Mr. A. B. Wynne, Mr. W. 

 Galloway, Mr. Joseph Dickinson, Mr. G. F. Deacon, Mr. E. 

 Wethered, Mr. A. Strahan, Professor Michie Smith, and 

 Professor H. L. Callendar, appointed for the purpose of investi- 

 gating the Rate of Increase of Underground Temperature downivards 

 in various Localities of Brij Land and Under Water. (JDrau-n ^ip 

 Inj Professor Everett, Secretarg.) 



Attention having been called to the copper-mining region on the south 

 coast of Lake Superior as exhibiting an exceedingly slow increase of 

 temperature downwards, the Secretary has availed himself of the kind 

 offices of Professor William Hallock, of Columbia University, to obtain 

 authentic information on the subject. Previous reports contain valuable 

 material furnished by Professor Hallock respecting a deep well at Wheeling, 

 in Virginia. 



The region in question is the most northerly portion of the State of 

 Michigan, and includes a tongue of land jutting out some sixty miles into 

 the middle of the lake, terminating in Keweenaw Point, which is marked 

 on all maps. The mine of the Calumet and Hecla Co^jpany, which is very 

 extensive, and has upwards of twelve shafts, is nearly in the middle of 

 this tongue ; and immediately adjoining it to the west is the Tamarack 

 mine, with live shafts. These two mines are about four miles from the 

 nearest coast (which is the north-west side of the tongue) and about eleven 

 miles from the south-east coast, the tongue being about fifteen miles wide 

 in this part. The ground is high, being 650 feet above the lake, which is 

 itself 600 feet above sea-level. The mineral veins dip to the north-west 

 under the lake, the dip ranging from 22° at the end of the tongue to 56° 

 at its root. The beds consist of a series of compact granular and amygda- 

 loidal traps, sandstones, and conglomerates. 



The latitude is 47°, and the mean annual temperature, according to 

 isothermal charts, is 39° or 40° F. The average depth of the lake is about 

 900 feet, and all the water below the depth of 240 feet was found, by 

 surveys conducted in the months of August and September, to be at about 

 39° F. As this is the temperature at which water has its maximum 

 density, it probably remains unchanged all the year round. The ground 

 beneath the lake is accordingly at a permanent temperature, practically 

 identical with the mean annual temperature of the air above, and the 

 boundai-y conditions for regulating underground temperature are practi- 

 cally the same as if all the water of the lake were removed and the air had 

 free access to the bottom. The slope of the bottom in the neighbourhood 

 of the mines in question is about 1 in 54 until a depth of 300 feet has 

 bhcn attained, and becomes gradually less steep to the depth of 700 feet. 



