152 



SCIENCE. 



[Vol. XI. No. 269 



and the coast of Cuba, — only a week after the ' Reindeer ' had 

 been dismasted about five hundred miles to the north-eastward. 

 There was a light breeze from the north-east at the time, and the 

 sky was about half covered with nimbus clouds, moving slowly. 

 Just after a light squall had passed by, the first appearance of a 

 water-spout was indicated by the formation of a whirlwind, grad- 

 ually increasing in size. It was cylindrical in shape below, spread- 

 ing out above, and rotating in a direction with the hands of a watch. 

 When within about a hundred yards of the vessel, its angular alti- 

 tude was about 35°, which would indicate a height of only two 

 hundred and fifty feet or less. It was moving to the south-west at 

 the rate of about eight miles an hour. At the base it was trans- 

 iparent ; and descending currents seemed to be plainly visible, 

 ■causing the water at the surface to fly in all directions. A heavy 

 shower of rain accompanied the spout, and the phenomena lasted, 

 dn all, about ten minutes. 



" Although the study of such reports has already greatly increased 

 our knowledge of the origin and nature of these interesting and 

 often destructive phenomena, much yet remains to be done before 

 we can hope to be able fully to understand the laws by which they 

 are governed. That portion of the North Atlantic from the north- 

 ern coast of Cuba to the 40th parallel, and from the Atlantic coast 

 ■of the United States to the Bermudas, is pre-eminently a region 

 where water-spouts are liable to occur, owing largely to the warm, 

 moist air which hangs over the Gulf Stream, and the cool, dry air 

 brought over it by the north-westerly winds from off the coast. 



" Among desirable observations to be made, referring to water- 

 spouts, special attention is called to the temperature of the air and 

 water, the reading of the barometer, direction and force of the 

 wind, and the changes which take place in each while the spout 

 lasts ; also the direction of rotation of the whirl, and an estimate of 

 its size, character, and changes of form, with, if possible, sketches, 

 however rough, of its appearance at the various stages of its forma- 

 tion and progress." 



SCIENTIFIC NEWS IN WASHINGTON. 



The Flow of Solids : Solids are not liquefied by Pressure. — The La-w 

 of Probabilities : a Discussion of the Doctrine of Philosophical 

 JSTecessity. — Dynamite Shells : the Progress made by the Ord- 

 nanc'e Department of the Arm-y with Experiments with Nitro-Glycer- 

 ine. 



The Flow of Solids. 

 Mr. William Hallock of the United States Geological Survey, 

 •whose paper upon a new method of making alloys was presented to 

 the Philosophical Society a few weeks ago, read another address 

 upon a somewhat related subject at the meeting of the same body 

 March 17. The question whether solids, he said in substance, 

 possessed any of the properties of liquids, or what conditions will 

 impart such properties to them, is one of ever-increasing impor- 

 tance, to the student alike of molecular physics in general, or of the 

 earth's crust in particular. 



The temperature rises as we penetrate the earth : hence, if no 

 •other influence affect the substances, the earth has a liquid centre 

 with a thin solid crust. Astronomical and mechanical facts seem 

 ■to demand a considerable rigidity. Thomson has even demanded 

 ■a. rigidity equal to that of glass or steel. Geological phenomena 

 require a considerable liquid-like motion. With rising tempera- 

 ture, as we penetrate the earth's crust, we also have rising pressure, 

 which probably increases the rigidity of the materials. Cannot we 

 satisfy the demands of both geology and astronomy, and also of 

 mechanics .'' 



In the glaciers we have the grandest examples of the flow of 

 solids. Henri Tresca proved that lead and some other substances 

 would flow, and follow the laws of flowing liquids^ W. Spring has 

 'extended the list. Monsson actually liquefied ice by pressure. 

 These observations have led many to advocate the idea of a lique- 

 faction by pressure. Others having in view the results of Bunsen, 

 Hopkins, Amazat, and others, maintain that the melting-point is 

 raised by pressure. 



Solids can be made to flow : hence that property cannot be used 

 to distinguish solids from liquids. The essential difference between 

 a solid and a liquid is that the relative ease of re-arrangement of 



the molecules in liquids is very easy, in solids very difficult. Ri- 

 gidity may be briefly defined as the difficulty of re-arranging the 

 molecules of the body in question. Can rigidity be reduced by 

 pressure? A priori, it seems scarcely likely that forcing the mole- 

 cules nearer together can give them greater freedom of motion. 

 Generally rigidity is inversely as the intermolecular distances. Ice 

 is abnormal, and cannot be taken as evidence pro or con. Lead, 

 copper, iron, steel, are all hardened by compression. All metals 

 are harder, more rigid, in the drawn, rolled, or hammered state 

 than cast or annealed. The rigidity of a steel pin was raised from 

 95,000 to 110,000 pounds per square inch by pressure. 



Two experiments were described bearing directly upon the 

 question, and are convincing, although they gave unwelcome re- 

 sults to those who made them. The first was conducted under 

 the direction of the Ordnance Department, and is given in full in 

 the report on ' Tests of Metals, etc., for 1884,' pp. 252-285. A 

 mixture of four parts wax and one part tallow was used as a 

 ' straining liquid ' in ' tangential ' test. It was demonstrated that 

 that mixture would not transmit pressure through a hole ^,, of <^^ 

 inch in diameter and 2i inches long, when the pressure at one end 

 was 100,000 pounds per square inch, and at the other 30,000 pounds 

 per square inch, or less ; whereas 2,000 pounds was sufficient to 

 overcome all friction, and force it through, when there was no back 

 pressure : that is, the wax and tallow were rigid enough, under 

 pressure, to maintain a difference of 70,000 pounds per square inch 

 (100,000 — 30,000) at the two ends of that hole. 



The second experiment was also made with the testing-machine 

 of the Ordnance Department at Watertown, Mass. (see American 

 Journal of Science, iii. 34, 1887, p. 280). In that experiment silver 

 coins on top of paraffine and beeswax in the holder, instead of sink- 

 ing through a liquid under 6,000 atmospheres, were pressed so hard 

 against the top of the holder that their impression in the steel was 

 easily seen and felt. The paraffine and wax vi'ere rigid enough to 

 impress silver into steel. 



Such facts lead us to believe that pressure increases rigidity ; 

 and, when we remember that the pressure at the centre of the earth 

 is millions of atmospheres, a demand for the rigidity of steel 

 seems trifling. What is the rigidity of steel? Simply a rigidity 

 capable of resisting 30,000 to 100,000 pounds per square inch. But 

 distinguished geologists have made the fatal mistake of using ' the 

 rigidity of steel ' and ' absolute rigidity ' as synonymous and equiv- 

 alent terms. Nothing is more misleading. 



Upheavals and depressions, and other geological phenomena, are 

 most beautiful examples of viscous flow of solids. The forces 

 causing a glacier to flow are trifling as compared with those gen- 

 erated in the earth's crust by shrinking ; and undoubtedly to cause 

 any body to flow, we only need sufiicient force and time. 



Can pressure impart to solids the ability to change crystallo- 

 graphically, mineralogically, chemically ? Prismatic sulphur naturally 

 changes to octahedral, and in many other cases changes take place 

 under ordinary conditions of pressure and temperature. We should 

 scarcely expect pressure pure and simple to cause a re-orientation 

 of the axes of the two crystal fragments, even if it could perfectly 

 weld them together. Nor should we expect pressure, without heat, 

 to impart the ability to complete the fusion of a lump of barium 

 sulphate in sodium carbonate, even after the process had been well 

 started by heat. Under the extremely complex conditions, it is dif- 

 ficult to generalize. A welding-together is not only theoretically 

 but practically possible between two chemically clean surfaces that 

 fit, but any operation which requires an increase of freedom in the 

 molecules would scarcely be assisted by pressure. Cohesion and 

 adhesion I believe to be identical, and molecular rather than molar. 



The bearing of these ideas, if good, upon geological phenomena, 

 is somewhat thus : by the action of pressure and time we might 

 find a sandstone, or such material, compacted, and rendered co- 

 herent or even continuous, the most plastic constituents yielding 

 most, and the most viscous retaining their shape most perfectly. 

 Some constituents might even appear to have been fused and filled 

 in between the rest. Certain crystallographic changes might take 

 place, but more than the slightest chemical effect of the constitu- 

 ents upon each other is not to be expected. The case becomes 

 infinitely complex, and a subject for conjecture only, if the tem- 

 perature is high. An indisputable fact in this connection is that 



