FOR GENERAL READERS. 



Vol. II. 



FRIDAY, AUGUST 10th, ih 



No. 6. 



Scientific Table Talk 



Reproduction of Articulate Speech and 



other Sounds (illus.) 

 Extinct British Butterflies. — I. 

 Simple Experiments in Physics — II. 



(illus.') 

 The Glacial Epoch and the Present Day 



General Notes 



Sun Dials, and How to Make Them. — 



I. Cillus.) 



Natural History : 



The Cobra (illus.) 



Notes on the Tiger 



Miscellaneous Notes 



PAGE 

 121 



122 



I2 4 



125 

 126 



129 



131 

 132 

 132 



CONTENTS. 



PAGE 



Locomotion of Caterpillars 132 



The Zoology of the Bath District. — I. 133 

 The Naturalist at the Sea-Side : 



IV. The Marine Aquarium ... 135 



Reviews : 



The Midland Naturalist 135 



A Handbook for Steam Users ... 136 

 Twelfth Annual Report of H.M. 



Inspectors of Explosives ... 136 



The Fig Trade 137 



Abstracts of Papers, Lectures, etc. : 



Royal Society 138 



Royal Horticultural Society ... 138 



Artificial Reproduction of Volcanic 

 Rocks 



Correspondence : 



Weather of July, I SS8— Alleged 

 Shower of Frogs — Whence 

 comes Man ?— Meteorological 

 Conundrums — Noises accom- 

 panying Auroral Displays ... 



Recent Inventions 



Sales and Exchanges 



Selected Books 



Notices... 



Meteorological Returns 



139 



141 



143 

 144 

 144 

 144 

 144 



SCIENTIFIC TABLE TALK. 



By W. Mattieu Williams, F.R.A.S., F.C.S. 

 Many still assume, as a matter of course, that all .colliery 

 explosions result simply from fire-damp, though Faraday 

 and Lyeil, in the Philosophical Magazine of 1845, report- 

 ing on their examination of a mine in which a great ex- 

 plosion had occurred, told us that " the coal-dust swept 

 by the rush of wind and flame from the floor, roof, and 

 walls of the works would instantly take fire and burn if 

 there were oxygen enough in the air present to support 

 its combustion ; and we found the dust adhering to the 

 face of the pillars, props, and walls, and in the direction 

 of and on the side towards, the explosion increasing gradu- 

 ally to a certain distance as we neared the place of igni- 

 tion. This deposit was in some places half an inch, in 

 •others almost an inch thick ; it adhered together in a 

 friable coked state." 



An examination of this deposit showed that it con- 

 sisted of partially burned coal-dust, which had been de- 

 prived of the greater part of its inflammable bitumen — 

 was in some cases entirely destitute of it. Faraday and 

 Lyell concluded that this coal-dust had been ignited, and 

 the extent of its combustion was limited by the supply 

 •of oxygen — that " much of the carbon of this dust re- 

 mained unburntonly for want of air." 



Mr. W. Galloway has more recently and quite inde- 

 pendently studied this subject very exhaustively, and has 

 proved that in many mines the dust is more dangerous 

 than the gas. The practical importance of the knowledge 

 which his researches have supplied is very great, even 

 greater than most mining engineers and other experts, 

 who only take into consideration the present operations 

 of coal-mining, suppose. 



1 base this opinion on the fact that we are rapidly ex- 

 hausting all the workable coal that exists at moderate 

 depths, and must go on sinking to deeper and deeper 

 seams until we are stopped altogether from further work- 

 ing, not by the exhaustion of the coal, but by the high 

 temperature rendering the operations of workmen, and 

 even the working of coal by machinery, impossible. 



When we get below a certain depth, which varies 

 greatly with the locality, the supply of water, which in 

 ordinary pits costs so much to remove, ceases ; the roads 



and workings become dry, and as every stroke of the pick 

 produces a certain amount of coal-dust, the accumulation 

 soon becomes considerable. The danger of such accumu- 

 lation is increased by the high temperature of the seam 

 itself, of the rock in which it is embedded, and of the 

 atmosphere of the workings. 



That an accumulation of dust may produce fearful and 

 fatal explosions without the aid of any fire-damp, or any 

 other explosive gas, has been proved again and again 

 by destructive explosions in flour-mills, although the 

 carbohydrates of the flour are less inflammable than the 

 hydro-carbons of the coal-dust; but, on the other hand, 

 the flour-dust is finer and lighter than ordinary coal-dust. 

 In the " Annales des Mines" for 1875 M. Vital describes 

 very minutely all the particulars of an explosion in the 

 Campagnac Colliery, 2nd November, 1874, where a shot 

 which blew out the tamping produced an explosion that 

 was fatal to three men. No fire-damp had been detected 

 there at any time, but the floor was covered with very 

 fine, dry coal-dust, the shot was fired at the bottom of 

 the face, and would thus raise a cloud of dust from the 

 floor. Other similar cases are recorded. 



The negative evidence in these cases is, however, not 

 always reliable. It is usually based on the behaviour of 

 the Davy lamp. The presence of fire-damp is indicated 

 by a " cap," which is a conical blue flame, more trans- 

 parent than the oil flame, and appearing to rest upon it. 

 The height of this cap varies with the quantity of fire- 

 damp mixed with the air. Mr. Galloway made a series 

 of experiments with measured artificial mixtures of these, 

 using a lamp-flame drawn down to about g inch high by 

 \ inch diameter at the base, and with only a conical 

 speck of yellow in the middle near the top (conditions 

 most favourable for showing a small cap). • He found 

 that 1 part of the inflammable gas to 16 of air gave a 

 voluminous, waving, spindle-shaped, pale-blue cap 3§ 

 inches high ; with 1 to 18 a similar cap 2 inches high, 

 which burned rather more steadily ; 1 to 20 a cap 1 ^fl- 

 inch high, with nearly parallel sides to about two-thirds 

 of its height, and drawn out to a point at the top ; 1 to 

 25 a conical cap k to^of an inch high; 1 to 30 a conical 

 cap § of an inch high ; 1 to 40 a conical cap ^ to \ 

 inch high ; 1 to 50 an exceedingly faint cap i of an inch 



