3jO 



SCIENTIFIC NEWS. 



[Sept. 28, l{ 



the longest incline of the wall, which extends from north 

 to south. 



These pools have accordingly received the name of 

 meridian-holes (irons meridionales). By their aid a 

 traveller in a fog, and without a compass, may at once 

 find his geographical bearings. 



It is easy to understand that this kind of excavation 

 may be carried on much further. So long as the water 

 can freely circulate, the warmer water will continue to 

 sink from the surface, and, when it is cooled down to 

 freezing point by its work of thawing, will rise again, 

 and this circulation may continue to any extent. In some 

 instances it does so continue for a long time, and thus 

 the little meridian hole grows to a deep, wide pit in 

 which some of the meridional features become partially 

 obliterated, but the elliptical form remains. On the 

 Unteraar glacier I saw several of these quite large 

 enough to justify the name given to them by our merry 

 mentors, who called them Baignoires, or bathing tubs, 

 and invited us to use them freely. Agassiz describes 

 examples reaching a length of 10 to 12 ft., a breadth of 

 3 to 4 ft., and depth of 20 ft. He calls them " Wasser- 

 bechcn," water basins. 



The ablation or thawing down of the glacier described 

 in my last necessarily supplies a large quantity of super- 

 ficial water. During the summer day-time the glacier 

 is alive with rills and streamlets of varying dimensions, 

 flowing along furrows of their own making, but their 

 course is usually short, in many glaciers very short. 

 They usually flow on until they reach a crevasse or 

 chasm, such as abound on the steeper glaciers ; then 

 pitch down this to contribute to the waters of the sub- 

 glacial tunnel which traverses the bottom of every glacier. 



But the Unteraar glacier being so nearly level has but 

 few crevasses, and these are far between ; therefore it 

 becomes easily possible for such rills to encounter a 

 baignoire. Two opposite results follow from this. If 

 the water of the streamlet is moderately clear it deepens 

 the pit, and may go on thus deepening it until it forms a 

 deep well in the ice, that may even reach to the bottom 

 of the glacier. This occurs when the quantity of clear 

 water is great. Such wells are named irons de cascade, 

 as when fully developed, and reaching the bottom 

 of glacier, all the water they contained in their bathing- 

 tub stage is drained away, and flows under the ice. 

 Thus the baignoire is converted into a deep hole with 

 perpendicular crystal sides, down one part of which an 

 eroding cascade is falling. Agassiz measured the depth 

 of one of these near to the Hotel des Neufchatelois, and 

 found it 260 metres (853 feet) deep, thus affording a 

 measure of the thickness of the ice at that part. 



If the rill that falls into the baignoire carries with it 

 much sand and gravel the butterfly's monument is 

 erected. How this comes about may in the meantime 

 stand as a physical problem for my readers to work out, 

 and compare their solution with that which I shall supply 

 next week. 



GASEOUS FUEL. 



A Paper Read by Mr. J. Emerson Dowson, M.Inst.C.E., 

 before the mechanical science section of the 

 British Association. 



(Continued from page 309.^ 



TO determine the working cost of a gas engine driven 

 with this generator gas, compared with a steam 

 engine and boiler, the more simple and direct way is to 



take in each case the weight of fuel used per h.p. per hour, 

 as it is no more necessary to determine the volume of gas 

 consumed than it is to know the volume ot steam used. 

 We have already seen that with this gas the fuel con- 

 sumption of several Otto engines doing practical work in 

 different places averages only i-J lbs. per indicated h.p. 

 per hour. The wages of the attendant, the cost of 

 repairs, and the other working expenses are about the 

 same as with a steam engine of equal power. The great 

 difference is in the consumption of fuel, and to make an 

 exact comparison I have taken the returns last published 

 by the Manchester Steam Users' Association, for all 

 engines indicating under 100 h.p., for which the net 

 fuel consumption is given. The details of these returns 

 will be found in Appendix II. of my Institution of Civil 

 Engineers paper before referred to, and from these it 

 appears that the average fuel consumption is 7 lb. per 

 indicated h.p. per hour. If, however, an average be taken 

 of 5 engines, each indicating 20 h.p., the fuel consumption 

 will be over n lb. per indicated h.p. per hour. It is 

 instructive too to note what Sir Frederick Bramwell said 

 on the fuel consumption of steam engines in actual work, 

 in his address (January, 1885) as President of the Institu- 

 tion of Civil Engineers. He said : — "In an investigation 

 instituted last year by the Corporation of Birmingham, 

 when considering whether they should approve of a pro- 

 posal to lay down power-distributing mains throughout 

 their streets, it was found on indicating some six non- 

 condensing steam engines, taken indiscriminately from 

 among users of power, and ranging from 5 nominal h.p. 

 up to 30 nominal h.p., that the consumption in one 

 instance was as high as 27*5 lb., while it never fell 

 below 9/6 lb., and the average of the whole was as much 

 as i8 - i lb. per indicated h.p. per hour." 



It is quite true that in competitive trials at the Royal 

 Agricultural Society's shows the fuel consumption of the 

 best portable engines working under the most favourable 

 conditions for a short time is slightly under 2 lb. per indi- 

 cated h.p. per hour, but this result can only be obtained 

 by the most careful nursing of the fire by highly-paid skilled 

 attendants who salt the fire, so to speak, with a slight 

 sprinkling of coal at very frequent intervals. In any 

 case we may safely say that with gas power the fuel con- 

 sumption under ordinary working conditions is at least 

 50 per cent, less than with non-condensing steam engines 

 of equal power. With gas there is the further advantage 

 that it can be conveyed to any part of the works without 

 appreciable condensation, that separate engines can be 

 used for different lines of shafting, and that any depart- 

 ment working overtime can have its engine supplied with 

 gas from a single generator. With steam, however, there 

 is much condensation if it be carried far, and much loss of 

 fuel if a large boiler has to be fired to keep a small 

 amount of shafting at work. 



I have so far confined my remarks chiefly to the appli- 

 cation of improved generator gas to motive power, and 

 there is no doubt that the recent departure in this branch 

 of mechanical science is one of great importance. I am, 

 however, glad to add that a considerable advance has also 

 been made in the use of this gas for heating of various 

 kinds. 



At the Gloucester County Asylum it has been in 

 daily use for a variety of purposes for about five years. 

 All the kitchen work for the staff and inmates is done 

 with it, and there is no ordinary fire in the kitchen. 

 About 300 quartern loaves are baked with the gas every 

 day at a cost of about one shilling only for fuel. The gas 



