May 21, 1886 ] 



SCIENCE. 



459 



in the Biologisches centralblatt. His attention 

 was directed to the subject by a simple incident. 

 Lying upon the floor of a hut near an open fire, he 

 noticed that the sky, as seen through a small win- 

 dow, seemed frequently lit up, as though by 

 lightning. Assuring himself that such was not 

 the case, he found that the apparent phenomenon 

 was due to a deception caused by the flickering- 

 light in the room, though no changes in its in- 

 tensity were visible. To show the effect more 

 strongly, he constructed a translucent shade be- 

 fore a lamp, upon which he attached a small disk 

 of thick white paper. This lamp was so arranged 

 that its brightness might be quickly and easily 

 varied. On the other side a gas-lamp enclosed by 

 an opaque cylinder was placed, emitting a ray of 

 light through a lens directly upon the paper disk. 

 Looking now at the disk through a hollow cylin- 

 der at a distance of several feet, while the light 

 behind the shade was made to vary in intensity, 

 there was found a striking effect, in that the varia- 

 tion appeared to rest only in the paper disk, while 

 the surrounding field appeared constant. This 

 illusion, the author says, shows that we are in- 

 clined to hold as constant the predominating 

 brightness in the field of vision, and attribute 

 variation to the subordinate. 



— It has been, experimentally proved by the 

 English commission on accidents in mines, as 

 stated in their last report, that a percentage of 

 marsh-gas amounting to five per cent, or even 

 four per cent, of atmospheric air, is decidedly ex- 

 plosive. Half of this proportion, however, though 

 not in itself dangerous, and though impossible of 

 detection by ordinary lamp-tests, will explode if 

 the air be laden even lightly with fine, dry coal- 

 dust ; and it is probable that some of the obscure 

 causes of accidents may be ascribed to this cause. 

 The opinion of the commissioners with regard to 

 the older Davy, Clauny, or even Stephenson 

 lamps, is that they have in a great measure lost 

 their value in consequence of the draughts of air 

 from the free ventilation. A current of air 

 of eight hundred feet per minute in an impure 

 atmosphere may, in spite of the wire gauze, effect 

 an explosion in any one of them. Electric light- 

 ing is already to some extent in use ; and as the 

 risk from its use is much less, and its lighting- 

 power greater, it probably will be more generally 

 adopted. 



— The summary report of the operations of the 

 geological and natural history survey of the Do- 

 minion of Canada by the director, A. R. C. Sel- 

 wyn, gives a creditable showing for the amount 

 of money expended. Work, chiefly geological and 

 topographical, has been prosecuted over portions 



of every province and territory in the dominion, 

 from Nova Scotia to the west coast of Vancouver 

 Island. The personnel of the survey is now com- 

 posed of a staff of fifty employees, — thirty-four 

 professional, and sixteen ordinary. The expen- 

 diture amounted to something over ninety thou- 

 sand dollars during the past year. The topo- 

 graphical results will be embodied in a number of 

 maps now in process of preparation. These maps 

 include one of British Columbia, that will shortly 

 be published ; one of Assiniboia, now in the hands 

 of the engraver ; and one of the Bow and Sas- 

 katchewan rivers, on a scale of eight miles to the 

 inch, well advanced. Another on Manitoba and 

 western Ontario, to cover 3,456 square miles, and 

 a very important geological map of the peninsular 

 portion of Ontario, to be issued in sheets of uni- 

 form size, are in progress, as well as maps of 

 Quebec, the Lake of Mistassini and adjacent re- 

 gions, and portions of Nova Scotia and New 

 Brunswick. Much less attention is paid to biolo- 

 gy, with the exception of paleontology ; yet in 

 botany and zoology considerable progress has been 

 made. Among the more interesting results of the 

 explorations is the determination of the size of 

 Lake Mistassini, about which there has been great 

 uncertainty. It was found to be about one hun- 

 dred miles in length, with an average breadth of 

 about twelve miles, — a very different figure from 

 what is represented on the maps. 



— Dr. Alfred Goldscheider, says the Lancet, has 

 recently published the results of researches he has 

 made upon the nerves, by which sensations of 

 temperature and pressure are conducted. He 

 finds that the skin is not in all parts capable of 

 perceiving variation of temperature, and that 

 some parts can only recognize sensations of cold, 

 other parts only sensations of heat. These, which 

 he terms warm and cold points, are distributed 

 between or among each other, but never coincide. 

 Their general arrangement is, that they are dis- 

 posed in chains which pursue a slightly curved 

 course. These chains radiate from certain points, 

 which may be termed radiation -points or tem- 

 perature-centres. The chains of the cold-points 

 do not in general coincide with those of the heat- 

 points, but these radiation-points are identical. 

 The cold-points are in all parts of the skin more 

 numerous than the warm-points. When the cold- 

 points are excited by either mechanical or electri- 

 cal stimuli, a punctiform sensation of cold is ex- 

 perienced, and the opposite sensation is felt when 

 the warm -points are stimulated. Goldscheider 

 was able, by stimulation of nerve-trunks, to ex- 

 cite eccentric sensations of heat and cold. The 

 temperature-points were found to be insensitive 



