3°6 



SCIENTIFIC NEWS. 



[Sept. 21, 1888. 



and the sun-rays were painfully scorching, as so fre- 

 quently is the case on the high Alps. 



On one of these snow peaks, the one showing the 

 fewest dark spikes of rock among the snow, thus present- 

 ing a cone of nearly unspotted whiteness, and named 

 accordingly the Point de Niege or Schneehorn, we saw 

 some dark moving specks like beetles crawling over the 

 snow. This was a section of the students that had made 

 the ascent, and were then on their way down. I was 

 surprised on their arrival to see several Alpine flowers 

 that they had collected from amidst this snowy desolation. 



Presently they started again as our guides over the 

 glacier, which differs materially from those that are more 

 familiar to the Alpine tourist, those of Chamouni, Grindel- 

 wald, etc. These are in steeply sloping valleys and 

 abound in crevasses, broken up angular masses of ice, and 

 general irregularities. The Aar glacier, at the part 

 chosen by Agassiz, and for a long distance both above 

 and below, has but a small slope, and thus the 

 action of the sun upon its surface has time to produce 

 some of its characteristic effects, which in steeper glaciers 

 become obliterated before they are fully developed. 



One of the first of these that we were shown was a 

 fine glacier table, a great block of stone perched upon a 

 cone of ice. Originally this stone had fallen from one of 

 the rock slopes flanking the glacier, and in its fall had 

 been projected beyond the lateral moraine, so as to stand 

 alone as a small island on the ice. In this position it 

 shaded the ice immediately below it, which thus retained 

 its original level while all around was thawing down. 

 The block and pedestal as we saw it presented at a dis- 

 tance the appearance of a gigantic mushroom. 



The time required for effecting a notable difference of 

 level will be understood by the following : — Agassiz 

 covered portions of the ice with different protecting sub- 

 stances, and observed the result at the end of 16 days. 

 A piece of woollen cloth stood not quite 8 ins. above the 

 naked ice ; an umbrella made a difference of 8f ins. ; a 

 wooden plank, 11 ins. ; a covering of turf, n| ins., and 

 of snow the same. Thus the general " ablation " or 

 thinning down amounted to about 1 ft. in the 16 days. 



M. Desor covered a space of 6 square metres with 

 turf on 15th July, and on 13th September found that the 

 glacier had sunk at an average rate of nearly i| ins. per 

 day. This of course varies with the season and weather. 



We were shown how to obtain our bearings by means 

 of a glacier table. The cone of ice on which it stands is 

 irregular, the slope of one side much greater than that of 

 the other. The longest slope is always on the north side 

 and the steepest on the south. 



The reason of this appears on a little reflection. The 

 sun at midday is due south, and during its most 'vigorous 

 working hours it is more or less southerly, and therefore 

 casts a due north and northerly shadow. It is the 

 shadow of the block of stone that protects the ice and 

 forms the cone on which the glacier table rests. 



For simplicity sake let us regard the work of the sun 

 at midday. Being on the south side of the block, and 

 below the zenith its rays must to some extent under- 

 mine the ice base, while the north side of the base is 

 completely in shadow. This goes on until such under- 

 mining causes the block to topple over to southward, 

 when it starts afresh to produce another glacier table. 

 In this way a huge block may actually travel across a 

 glacier. Agassiz saw one that was 15 ft. long, 12 ft. 

 wide, and 6 ft. high, slide 30 ft. on falling. It reduced 

 to powder the ice over which it passed. 



GASEOUS FUEL. 



AP aper Read by Mr. J. Emerson Dowson, M.Inst. 

 c.e., before the mechanical science section of 

 the British Association. 



A T the York meeting of the Association, in 1881, I had 

 •** the privilege of explaining for the first time an 

 apparatus with which I had succeeded in making a cheap 

 fuel-gas, and I gave the economical results of working 

 some gas engines with it. An abstract of my paper will 

 be found in the Transactions of Section G. Since then 

 I have gained a much wider experience in connection 

 with this subject. My apparatus has been considerably 

 improved, and the gas made in it has been much used, 

 not only for driving engines but for heating in many in- 

 dustrial processes. I propose, therefore, to give a short 

 account of the development which has taken place, and 

 of some of the more important results obtained: 



Like other generator gas, mine is made by passing 

 steam and air through incandescent fuel, and gas so 

 made can be taken direct from the generator and burnt 

 in a furnace without being purified or cooled. For such 

 work large flames are used, and it is comparatively 

 easy to deal with them. When, however, the gas is 

 required for a gas engine, or for small burners, the con- 

 ditions are very different. The gas must be clean, or 

 troublesome deposits will occur in the pipes and cocks, 

 and it must pass through a gasholder to insure uni- 

 formity of pressure in the distributing pipes. It must 

 also be cool, and this is especially the case for gas 

 engines, as within certain limits the cooler and denser 

 the gas, the greater is the energy in the limited volume 

 which can enter the cj'linder. It is also essential that 

 when small jets of gas are used, as in small burners, 

 the gas should be fairly strong and of uniform quality, 

 or the flames will not burn steadily. To any one accus- 

 tomed to the manufacture of ordinary lighting gas, these 

 remarks may perhaps seem too elementary, but it should 

 be remembered that generator gas is usually required in 

 large quantity, and that to avoid large gasholders, it 

 should be made as quickly as it can be consumed. In 

 one case I have had to provide plant to make gas at the 

 rate of one million cubic feet per day, or about 90,000 

 cubic feet per working hour, and without expensive 

 appliances the cooling and cleaning of so large a volume 

 of gas is not so simple as it may at first sight appear. 



The original invention dealt with the generator only, 

 but I have since found it necessary to devise a complete 

 set of gas plant, to meet the requirements of practical 

 work. In nearly all cases it is important that the appa- 

 ratus should occupy as little room as possible, and the 

 accompanying figs. 1 and 2 show the arrangement usually 

 adopted. The steam boiler is small and specially made 

 with a super-heating coil, so that dry steam enters the 

 generator. The gas from the generator passes through 

 water in the washer, and then through a scrubber con- 

 taining coke moistened by water. The scrubber is placed 

 inside the gasholder tank, so as to occupy as little ground 

 space as possible. The rise and fall of the gasholder is 

 made to regulate the supply of steam to the injector, so 

 that to a certain extent the production of gas can be regu- 

 lated automatically to suit a varying rate of consumption. 

 In some special cases the gas is passed through oxide of 

 iron to remove all traces of sulphuretted hydrogen, but 

 for general purposes chemical purification is not neces- 

 sary. The whole is very compact, and a plant large 

 enough to drive an engine of 50 h.p. indicated, occupies 



