Augusi 25, 1881] 



NATURE 



value from observations of Mars is 8"78, agreeing exactly 

 with Michelson's light velocity and the mean constant of 

 aberration. Some other astronomers favour a higher 

 value of the solar parallax, such as 8" 86 ; but whichever 

 value we adopt, and whether we prefer Cornu's or Michel- 

 son's determination of the light velocity, the conclusion 

 is that there can be no such difference between the group 

 velocity and the wave velocity as 2 or 3 per cent., unless 

 indeed the usual theory of aberration requires serious 

 modification. These considerations appear to me to 

 increase the already serious difficulties, which cause hesi- 

 tation in accepting the views of Young and Forbes. The 

 advent of further evidence will doubtless be watched with 

 great interest by scientific men. 



One other point I may refer to in conclusion. Specu- 

 lations as to harmonic relations between various spectral 

 rays emitted by a glowing gas proceed upon the assump- 

 tion that the frequency of vibration is inversely propor- 

 tional to the wave-length, or, in other words, that the 

 velocity of propagation V is independent of the wave- 

 length, the question now at issue. If the views of Young 

 and Forbes are correct, calculations of this kind must be 

 overhauled. On the other hand, the establishment of 

 well-defined simple ratios between wave-lengths would 

 tend to show that Fdoes not vary. Rayleigh 



August IS 



ELECTRIC LIGHT IN COLLIERIES 



AUGUST 9, 1881, witnessed the first practical applica- 

 tion in the United Kingdom of the electric light to 

 the illuminating of coal-mines. The Earnock Colliery, 

 near Hamilton, Lanarkshire, belonging to Mr. J. Watson, 

 has been fitted with Swan's incandescent lamps specially 

 arranged with outer lanterns of stout glass, air-tight, and 

 provided with steel guards. The workings in which the 

 lamps were fixed are 118 fathoms, or 708 feet below the 

 surface. Twenty-one brilliant little lights placed at the 

 pit-bottom, in the roads, and at the actual face of the seam 

 where active operations were in process, supply an illu- 

 mination of a very dilTerent character from the dismal 

 glimmer of an occasional Davy. The electricity was 

 generated by a dynamo-electric machine at the surface 

 worked by a special 12 horse-power engine, and conveyed 

 by two cables, first along telegraph poles to the pit mouth, 

 then down the shaft to the workings, in one section to a 

 distance of half a mile. The overhead wires are naked 

 copper wires of g inch diameter, while those below ground 

 are carefully insulated, and in the shaft are protected with 

 an outer tube of galvanised iron. At suitable points of 

 the circuit safety air-tight switches, the invention of 

 Messrs. Graham of Glasgow, are inserted to afford control 

 over individual lamps. The mine was visited two days 

 after the installation of the light by members of the 

 Mining Institute of Scotland, with whom was Mr. W. 

 Galloway, whose remarkable experiments on the explosive 

 effects of coal-dust will be remembered in connection with 

 the more recent report of Prof. Abel. The party were 

 photographed in the workings. An experiment was made 

 with a lamp to test whether in the event of its being 

 broken by accident a surrounding atmosphere of explosive 

 gas would or would not be kindled by the strip of red-hot 

 carbon before it had had time to cool. Into a box con- 

 taining about three cubic feet of explosive gas a single 

 lamp, removed from its outer protecting case of stout 

 glass, was placed, and the current was turned on. The 

 fragile bulb inclosing the incandescent carbon thread was 

 then purposely broken, when the gas inclosed in the box 

 immediately exploded. No such occurrence could possibly 

 happen if the protecting case of stout glass is properly con- 

 structed. The risk of accident must be considered as 

 immensely less than that of the ordinary Davy lamp, 

 especially when it is remembered that w-ith the brilliant 

 light of the electric lamps they need no longer be carried 



in the hand or set down upon the floor near the actual 

 spot where the coal is being got, but willbefi.xed overhead 

 at a safe distance against the wall of the mine. The ease 

 with which the light can be turned out during the firing 

 of a blast is another point in their favour. The proprietor 

 of the Earnock Colliery is greatly to be congratulated on 

 the step he has taken. In 1880 the death-roll of the slain 

 by explosions of fire-damp in Great Britain reached the 

 figure of 499 persons. We venture to predict that the 

 universal adoption of electric lighting in fiery mines would 

 reduce this figure to one-tenth of its terrible proportions. 

 How many years will it be, we wonder, before the adop- 

 tion of electric lighting will be made compulsory by Act 

 of Parliament .■■ And how many colliery owners will dis- 

 cover, we would ask, when driven to this course by com- 

 pulsion, that in the long run they effect an economy by 

 discarding the clumsy and unsafe " safety "-lamp, which 

 will so soon be numbered with the " flint mill " amongst 

 the relics of the past? 



SINGULAR STONE HATCHETS' 



MONSIEUR PITRE DE LISLE has lately called 

 attention to a singular class of stone celts or 

 hatchets which have for the most part, if not indeed only, 

 been found in Brittany and North- Western France. 



These hatchets, instead of tapering away to a more or 

 less conical point at what has been termed the butt-end, 

 suddenly expand close at that part, so as to present a 

 somewhat button-like termination. In one instance, at 

 least, the hatchet ends in a spheroidal ball not unlike that 

 which one occasionally sees on the horns of cows which 

 are inclined to make too free use of their natural arms of 

 offence. In the case of the hatchets, however, the button 

 is at the opposite end to that which was in use for cutting. 

 These blades vary in length from about three inches to 

 as much as fifteen inches, and are all made of rocks 

 belonging to the family of Diorites, principally of 

 Aphanite. 



M. de Lisle has given to these instruments the name of 

 " haclifs A tite" ox '■'■ haches d //ou/o/i," and has pointed 

 out the similarity which in some respects they bear to 

 hatchets of Carib origin and to the />u-n's of New Zea- 

 land. In these instances the object in view in fo- - ' ^ a 

 projecting rib round the end of the blade was no doubt 

 to aftbrd the means of preventing it from slipping out of 

 the handle or hand which held it. He thinks that the 

 same object led the makers of these French blades to 

 adopt the same form, and that the hatchets, after passing 

 through a transverse hole in their hafts, were secured by 

 cords wound around them, which abutted against the 

 projecting rims at their small end. In his opinion there 

 is a representation of this method of hafting to be seen 

 among the sculptures on the dolmen of Mand-Lud. 



It is a remarkable circumstance that the hatchets of 

 this particular form appear to be restricted to so small a 

 district of France, and not to occur elsewhere. M. de 

 Lisle is in consequence inclined to assign the develop- 

 ment of this type to a late period in the Neolithic age, 

 and has offered some reasons for inferring that in Brittany 

 the use of bronze hardly found a home, and that stone 

 was the principal material employed' for cutting tools 

 when first that part of Gaul was brought in contact with 

 Roman civilisation. It seems probable enough that in 

 that as in other countries there were districts which lay 

 far away from the principal highways of progress and 

 civilisation, and where old-world usages prevailed long 

 after material advances had been made in more fortunate 

 but not very distant regions. 



\\' e may however be allowed to doubt whether the 

 country of the Veneti, the most enterprising maritime 

 tribe of Gaul, whose ships in the days of Julius Csesar 

 were already provided with chain-cables of iron, were 



■ " Les Haches i Tete de la Eretagne, etc." (Nantes, 1880.) 



