Nov. 25, 1881.] 



KNOWLEDGE ♦ 



67 



when at just aliout the temperature of freezing, but not if 

 much colder. Tyndall has further illustrated this by 

 taking fragments of ice and squeezing them in a mould, 

 whereby they became a clear, transparent ball, or cake, 

 and schoolboys did the like long before when snowballing 

 with snow at about the thawing point Such snow, as we 

 all remember, became converted into stony lumps when 

 firmlv pressed together. We also remember that iu much 

 colder weather no such cohesion occurred, but our snow- 

 lialls remained powdery in spite of all our squeezing. 



1 am a sceptic as regards regelation. I believe that the 

 true e.xplanation is much simpler ; that the crystals of 

 snow or fragments of ice in these experiments are simply 

 welded, as the smith unites two pieces of iron, by merely 

 pressing them together when they are near their melting 

 ' point. Other metals and other fusible substances may be 

 similarly welded, provided they soften or become suffi- 

 ciently viscous before fusing. Platinum is a good example 

 of this. It is infusilile in ordinary furnaces, but becomes 

 pasty before melting, and, therefore, one method adopted 

 in the manufacture of platinum ingots or bars from the 

 ore, is to precipitate a sort of platinum snow (spongy 

 platinum) from its solution in acid, anil then compress this 

 metallic snow in red hot steel moulds by means of pistons 

 driven with great force. The flocculent metal thus be- 

 comes a solid, coherent mass, just as the flocculent ice 

 became coherent ice in Tyndall's experiment or in making 

 hard snowballs. Wax, pitch, resin, and all other solids 

 that fuse, gradually cohere, are weldable, or, in very plain 

 language, " stick together " when near their fusing point. 



I have made the following experiment to prove that 

 when this so-called regelation of snow or ice fragments 

 occurs, the ice is ^^scous or plastic, like wax or pitch. A 

 strong iron squirt, with a cylindrical Ijore of half-an-inch 

 in diameter, is fitted with an iron piston. Tliis piston is 

 driven forth bj- a screw working in a collar at one end of 

 the squirt. Into the other end is screwed a brass nozzle 

 with an aperture about one-twentieth of an inch diameter, 

 tapering or opening inwards gi-adually to the half-inch 

 bore. 



Into this bore I place snow or fragments of ice, then 

 holding the body of the squirt firmly in a vice, I work the 

 lever of the screw, and thus drive forward the piston and 

 crush down the snow or ice fragments, which presently 

 become coherent and form a half-inch solid cylinder of clear 

 ice. Applying still more pressure, this cylinder is forced like 

 a liquid through the small orifice of the nozzle of the squii-t, 

 and jets or sprouts out as a thin stick of ice like vermicelli, 

 or the '• leads "' of ever-pointed pencils, for the moulding 

 of which the squirt was originally constructed. 



I find that ice at 32° can thus be squirted more easily 

 than bees'-wax of the same temperature, and such being the 

 case, I see no reason for imagining any comple.x operation 

 of regelation in the case of the ice, but merely regard the 

 adhesion of two pieces of ice when pressed together as 

 similar to the sticking together of two pieces of coblilers'- 

 ■wax, or softened sealing-wax, or bees'-wax, or the welding 

 of iron or glass when heated to their welding temperatures, 

 i.e., to a ceiiain degree of incipient fluidity or viscosity. 



If a leaden bullet be cut in half, and the two fresh-cut 

 faces pressed forcibly together, they cohere at ordinary 

 atmospheric temperatures, but we have no occasion for 

 regelation here. The viscosity of the lead accounts for all. 

 At Woolwich Arsenal there is a monster squirt, similar to 

 my little one. Tliis is charged with lead, and, by means of 

 hydi-aulic pressure, the lead is squirted out of the nozzle as 

 a cylindrical jet of any required diameter. This jet or 

 stick of lead is the material of which the elongated 

 cylindrical rifle bullets are now made. 



But returning to the point at which we started, on the 

 subject of ice, viz., its Alpine accumulation above the 

 snow-line. If the snow-fall there exceed the amount that 

 is thawed and evaporated, it must cither go on growing 

 upward until it reaches the highest cloud, or atmospheric 

 region, from which it falls, or is formed, or it must descend 

 somehow. 



If ice can be squirted through a syringe by mere hand- 

 pressure, we are justified in expecting that it would be 

 forced down a hUl slope, or through a gully, or across a 

 plain, by the pressure of its own weight when the accumu- 

 lation is great. Such is the case, and thus are glaciers 

 formed. 



They are, strictly speaking, rivers or torrents of ice ; 

 they flow as liquid water does, and down the same channels 

 as would carry the liijuid surface drainage of the hills, were 

 rain to take the place of snow. Like rivers, they flow 

 with varying speed, according to the slope ; like rivers, 

 their current is more rapid in the middle than the sides ; 

 like rivers, they exert their greatest tearing force when 

 squeezed through narrow gullies ; and, like rivers, they 

 spread out into lakes when they come upon an open basin- 

 like valley, with narrow outlet. 



The Justedahbrae of Norwaj- is a great ice-lake of this 

 character, covering a surface of about -500 square miles, and 

 pouring down its ice-torrents on every side, wherever there 

 is a notch or valley descending from the table-land it covers. 

 The rate of flow of such downpouring glaciers varies from 

 two or three inches to as many feet per day, and they 

 present magnificent examples of the actual fluidity or 

 viscosity of an apparently solid mass. This viscosity has 

 been disputed, and attempts have been made to otherwise 

 explain the motion of glaciers, but while it is possible that 

 it may be assisted by varying expansion and contraction, 

 the downflovi- due to viscosity is now recognised as unques- 

 tionably the main factor of glacier motion. 



Cascades of ice may be sometimes seen. In the course 

 of my first visit to Norway, I wandered alone over a very 

 desolate mountain region towards the head of the Jnstedal, 

 and unexpectedly came upon a gloomy lake, the Styggevand, 

 which lies at the foot of a precipice-boundary of the great 

 ice-field above-named. Here, the ice having no sloping 

 valley-trough by which to descend, poured over the edge of 

 the precipice as a great overhanging sheet or cornice, which 

 Vient down as it was pushed forward, and presented on 

 the convex side of the sheet some tine blue cracks, or 

 " crevasses " as they are called. These gradually widened 

 and deepened, until the overhanging mass broke oft" and 

 fell into the lake, on the surface of which I saw the result, 

 in the form of several floating icebergs that had previously 

 fallen. 



Something like this on a small scale may be seen at 

 home on the edge of a house roof, on which there has been 

 an accumulation of snow ; but, in this case, it is rather 

 sliding than flowing that has made the cornice ; but its 

 down-bending is a result of viscosity. 



GERMS OF DISEASE AND DEATH. 



By Dr. Andrew Wilson, F.RS.E. 



MOST readers have heard of the " Germ theory," and 

 there are few persons who do not know what the 

 hypothesis of that name means and implies. Popularly 

 regarded, this theory holds that a very large proportion of 

 the diseases that aflect and afflict man and his neighbour 

 animals, owe their origin to minute forms of life — whether 

 animal or vegetable, or both, is still, in most cases, a 



