194 



SCIENTIFIC NEWS. 



[Aug. 31, 18 



Why should one such valley be an avalanche track, and 

 another be occupied by a glacier ? 



This is a question that is rarely asked or answered, 

 although instances abound of such discrepant valleys lying 

 side by side, and both communicating with the same nevt. 

 Thoughtful observation of such discrepancies presents a 

 solution of the problem. 



The avalanche valleys widen downwards, those which 

 are filled with glacier ice are narrower below. In a few 

 rare cases a dam or barrier of rock does the work of 

 general narrowing. 



The effect of such narrowing of a trough or valley out- 

 let of the snow is easily understood. An avalanche 

 falling down a widening furrow or valley is outspread 

 as it descends, and thereby exposes a large surface to the 

 summer sun ; that falling into a narrowing furrow lodges 

 and accumulates in a thick heap below, which may or 

 may not, according to its quantity, be able to resist the 

 summer thawing. If not, it disappears in the autumn, 

 to be replaced next year by a similar evanescent accu- 

 mulation. 



If, however, the quantity is greater than the summer 

 sun can thaw, more or less remains ; to this is added 

 the next year's accumulation, and so on until the valley 

 is filled, and its contents become continuous with the 

 neve above. Then a true glacier is completed, which there- 

 after flows downwards in a continuous stream of appa- 

 rently solid, but actually semi-fluid or viscous, ice, dis- 

 playing in its course a series of most interesting pheno- 

 mena due to the exposure of a large mass of ice that has 

 descended far below the snow line, and is consequently 

 in a state of continuous thaw during the summer days, 

 and is continuously replenished by silent and invisible 

 downflow from above. 



My attention was first directed to the birth-his- 

 tory of glaciers in the course of a walk up 

 the Romsdal, by observing that in nearly all the 

 breaks and hollows of the Troltinderne there were 

 patches of snow, some of them so low as almost to touch 

 the oat-fields. I was puzzled by their position, only a 

 few hundred feet above the sea in the latter part of 

 summer, and with a nearly south aspect, but presently I 

 observed that some of the multitude of distant cascades 

 were temporary ; further observation showed that they 

 were not waterfalls as I first supposed, but snowfalls, that 

 suddenly ceased, and were followed by a low thunderous 

 rumble that settled the question of their composition. 

 Below all these were .patches or pockets of snow that 

 only required a sufficient supply from above to become 

 full-grown glaciers, and from which actual glaciers will 

 ultimately become evolved, if the present conditions 

 remain long enough, for these small avalanches have 

 visibly rasped and smoothed and deepened the gully 

 down which they fall, and are thereby continually deepen- 

 ing and narrowing it, while at the same time enlarg- 

 ing the upper outlet b3^ their aid to ordinary frost and 

 thaw weathering. 



Another lesson may here be learned, viz., that a series 

 of avalanches may do the work of smoothing, and groov- 

 ing, and striation, and moraine heaping, usually ascribed 

 without discrimination — even by our best geologists — 

 to glaciers. 



I described these in " Through Norway with a Knap- 

 sack," chapter x. In Tonsberg's "Illustrated Hand- 

 book," published sixteen years later, is a picture of the 

 Troltinderne, showing some of the low snow patches and 

 a large outspreading avalanche talus. 



ICE-MAKING MACHINE. 



REFRIGERATING machines are now very largely 

 used for preserving meat and other articles of food, 

 for cooling or regulating the temperature of air or water, 

 for the production of ice, and for many other industrial 

 purposes. In the steamships which convey meat from 

 Australia, New Zealand, and other countries, the re- 

 frigerators are nearly always kept at a low temperature 

 by means of air pumps, the cold being produced by the 

 expansion of the air previously compressed. Ammonia 

 and ether are also used, as they vapourise under the 

 ordinary atmospheric pressure at a low temperature, 

 and in the process of vapourising a large amount of heat 

 is rendered latent, and thus cold is produced. Ether is, 

 however, more troublesome to deal with, and its use is 

 attended with greater expense, so that ammonia is more 

 generally adopted. There are machines in which 

 ammonia gas is compressed mechanically into the liquid 

 state, and this liquid ammonia is afterwards vapourised 

 so as to produce a low temperature. Another system, 

 much used by brewers and others, is to obtain the re- 

 quired anhydrous liquid ammonia from the ammoniacal 

 liquor of commerce, by the application of heat and subse- 

 quent condensation. 



It is on this principle that the well-known refrigerating 

 machine made by Messrs. Pontifex and Wood is worked. 

 In a strong horizontal cylinder or generator a charge of 

 the ammoniacal liquor of commerce is placed. In this 

 cylinder there is a coil of piping through which steam is 

 passed, and the ammonia is driven off by the heat of the 

 steam. The ammonia then passes through a separator, 

 in which any vapour of water which rises with it is con- 

 densed and returned to the generator. From the separator 

 the ammonia gas is conveyed to a condenser, consisting 

 of a cylinder containing a coil of piping through which 

 there is a circulation of cold water. In this condenser 

 the ammonia is condensed into the liquid form, and this 

 liquid ammonia is then passed into another cylinder, 

 called a cooler. When it enters the cooler the liquid 

 ammonia has a temperature of 70 to 8o° F., and it is 

 then allowed to expand into the gaseous form. In doing 

 so its sensible heat is rendered latent, and its temperature 

 is usually reduced to about io Q or 20? F., say 22 to 12 

 degrees below freezing. In the cooler there is a coil of 

 piping, through which water or brine is circulated, and 

 the expanding ammonia gas cools this water or brine 

 down to any required temperature. When the ammonia 

 has expanded, it has done all the work of cooling which 

 it is capable of, and it is then collected and again passed 

 into the first cylinder or generator, to be used over again. 

 The process is a ,very interesting one, the same water 

 and the same ammonia being used repeatedly, and 

 the changes of condition being regulated by the 

 application of heat and cold as described. 



The water or brine which is cooled by the expansion 

 of the ammonia can be used for a variety of purposes. 

 In breweries, for instance, the cold water required is 

 passed direct through the coil in the cooler. For ice- 

 making a strong solution of common salt is used instead 

 of water as the circulating medium, as it freezes at a 

 lower temperature, and after this brine has been reduced 

 to a very low temperature by passing through the 

 cooler, it is made to circulate through the ice tanks, and 

 then to return to the cooler to be re-cooled for further 

 use. The ice-boxes are of various forms, but the prin- 

 ciple on which their working depends is the same in all 

 of them. 



