August 22, 1901] 



NA TURE 



599 



sealing-wax. This partly defeated the aim of the experiment 

 (to find the temperature of the upper part of the stone), since 

 only the mean temperature was found. This mean temperature 

 of the hottest stone of the upper layer, as deduced from the 

 above data, was about 1200 degrees Fahrenheit, but the 

 temperature of the surface must h.^ve been indefinitely lower. 

 The temperature at which such a stone begins to show a dull 

 ted in daylight is, so far as I am aware, not exactly determined, 

 but is approximately 1300 to 1400 degrees Fahrenheit. 



To conclude, I could entertain no doubt that I had witnessed 

 substantially the scenes described by the gentlemen cited, and I 

 have reason to believe that I saw a very favourable specimen of a 

 " Fire Walk." 



It was a sight well worth seeing. It was a most clever and 

 interesting piece of .savage magic, but from the evidence I have 

 just given I am obliged to say (almost regretfully) that it was 

 not a miracle. S. P. Lanulev. 



Smithsonian Institution, Washington, D.C., August 7. 



The Size of the Ice-grain in Glaciers. 



In" referring to the size of the grain of the glacier in the 

 chapter on chemistry and physics in the "Antarctic Manual," 

 I have given 700 grammes as the maximum weight which I have 

 observed. In August, 1S95, I made an extended study of the 

 structure of glacier ice, principally from the .\letsch Glacier. 

 The fragments of this glacier, which float as icebergs in the 

 Mergelin See, are exposed to the powerful weathering influence 

 of the summer sun, and are comparatively easily dissected into 

 their constituent grains. A number of blocks were so dissected 

 in order to asceriain the weight and size of the largest grains. 

 The following weights of single grains were determined ; — 700, 

 590, 450, 270, 255, 170, I55and 100 grammes. It was observed 

 that blocks of ice contained grains of all sizes, which fitted each 

 other so exactly that, in the fresh unweathered block, the whole 

 voluine was filled with ice. 



It was not then thought necessary to determine the weight of 

 the smaller grains. On revjsiting the Mergelin See in the 

 latter part of July of this year, I dissected several blocks of ice 

 more or less completely and weighed their constituent grains. 

 In order to effect the dissection a powerful sun is requisite, and 

 a powerful sun means a high atmospheric temperature, under 

 the influence of which the small grains melt and disappear very 

 cjuickly. All the grains in the block are melting at the same 

 time, but the smaller the grain the greater is the ratio of its 

 external surface to its mass. Therefore the weights of the large 

 grains are reduced in a less degree than those of the small ones. 

 Hence it is impossible to furnish an e.xact statistical account of 

 any block of ice, but the figures in the following tables give a 

 very fair idea of the structural composition of the ice examined. 

 The analyses of blocks E and F are the most complete. 



The first block. A, is from the lower end of the C'dacier des 

 Bossons in the Chamonix valley, and it was examined on July 

 17, 1901, which was one of the hottest days of that very hot 

 week. The other blocks are all from the Aletsch Glacier, as they 

 are found floating in the Mergelin See, the waters of which are 

 retained at one end by the ice of that glacier. The Aletsch 

 Glacier is the largest in Switzerland and it contains the largest 

 ice-grains that I have met with. Different parts of the glacier, 

 even in the immediate vicinity of the lake, are of diflerent grain, 

 and the fragments are easily distinguished as they float in the 

 water. Thus block F is a block of large grained ice, while E is 

 of comparatively small grained ice, though it is by no means of 

 the smallest grain. 



List of blocks dissected. 



Block A. — Chamonix, July 17, 1901. From the end of the 

 (Hacier des Bossons. 



Blocks B, C and D were taken from the Mergelin See on 

 July 21, 1901, and exposed to the sun on a rock for some hours. 

 B and C were then dissected, though not completely ; that is, a 

 certain comparatively small portion of each of them remained 

 undissected. D was dissected only in so far as to enable a 

 prominent and very large grain (570 grm.) to be removed and 

 weighed. The remainder was left till the next day. Owing to 

 the high temperature of the air both by night and by day, its 

 size was very much reduced. It is called Block d, and it was 

 dissected on July 22, 1901. 



Block E from the Mergelin See was collected and dissected 

 on July 22, 1901. 



Block F had suffered far-reaching sun weathering. It was 



NO. 1660, VOL. 64] 



not removed from the lake, but was dissected in the water on 

 July 24, 1901. 



The results are embodied in the two following tables. All the 



Weight, in grammes of single ice-grains. 



