265 



SCIENTIFIC SIDE-LIGHTS 



Force 



water, which as a liquid is to all appear- 

 ance formless. When sufficiently cooled the 

 molecules are brought within the play of the 

 crystallizing force, and they then arrange 

 themselves in forms of indescribable beauty. 

 TYNDALL Forms of Water, 88, p. 30. 

 (A., 1899.) 



1292. FORCE OF EXPANSION RE- 

 SISTLESS Freezing Water Shatters Iron. 

 The force with which water expands in 

 freezing is all but irresistible. With the 

 view of giving you an illustration of this 

 fact, water has been confined in this iron 

 bottle which is fully half an inch thick; 

 the quantity of water being small, tho suffi- 

 cient to lill the bottle. The bottle is closed 

 by a screw firmly fixed in its neck. Two 

 bottles thus prepared are placed in a copper 

 vessel, and surrounded with a freezing mix- 

 ture. They cool gradually, the water within 

 them approaching its point of maximum 

 density. No doubt, at this moment, a small 

 vacuous space exists within each bottle. 

 But soon the contraction ceases, and expan- 

 sion sets in. The vacuous space is slowly 

 filled, the water gradually changes from 

 liquid to solid. To accomplish this change 

 it requires more room, which the rigid iron 

 refuses to grant. But its rigidity is power- 

 less in the presence of these molecular 

 forces, and the sound you now hear indi- 

 cates that the bottle is shivered by the crys- 

 tallizing molecules. The other bottle fol- 

 lows; and here are the fragments of the 

 vessels, showing their thickness, and im- 

 pressing you with the vastness of the expan- 

 sive force by which they have been thus 

 riven. While I have been speaking, you 

 have heard a louder explosion in front of 

 the table. That was due to the rupture of 

 a thick bombshell kindly prepared for me at 

 Woolwich by Professor Abel. It was filled 

 Avith water, screwed up tight, placed in a 

 bucket, and surrounded by a freezing mix- 

 ture. Taken from the mixture, the frag- 

 ments of the bomb are placed here before 

 you. Care must be taken in repeating this 

 experiment to cover the bucket with a thick 

 cloth. Wanting such protection I have seen 

 the stopper of a broken bomb projected 

 nearly as high as this ceiling. TYNDALL 

 Heat a Mode of Motion, lect. 4, p. 105 (A 

 1900.) 



1293. FORCE OF GRAVITY AT THE 



SUN'S SURFACE The sun attracts ob- 

 jects at its surface twenty-seven times more 

 strongly than the earth does. This calcula- 

 tion would be the same for the investigation 

 of gravity at the surface of all the planets. 

 A human body, if it could be transported to 

 the sun, would be immediately flattened by 

 gravity into a thin leaf. But, in point of 

 fact, it would be vaporized long before it 

 could arrive there. FLAMMARION Popular 

 Astronomy, bk. iii, ch. 2, p. 242. (A.) 



1294. All Earthly Ad- 

 justments Changed. If we calculate the 

 force of gravity at the sun's surface, which 



is easily done by dividing its mass, 330,000, 

 by the square of 109y 2 (the number of times 

 the sun's diameter exceeds the earth's), we 

 find it to be 27 % times as great as on the 

 earth ; a man who on the earth would weigh 

 150 pounds would there weigh nearly two 

 tons; and, even if the footing were good, 

 would be unable to stir. A body which at 

 the earth falls a little more than 16 feet in 

 a second would there fall 443. A pendulum 

 which here swings once a second would there 

 oscillate more than five "limes as rapidly, 

 like the balance-wheel of a watch quiver- 

 ing rather than swinging. YOUNG The Sun, 

 ch. 1, p. 41. (A., 1898.) 



1295. FORCE OF RUNNING WATER 



Sand and Pebbles Give -Cutting Power. 

 The mechanical force exerted by running 

 water in undermining cliffs and rounding 

 off the angles of hard rock is mainly due to 

 the intermixture of foreign ingredients. 

 Sand and pebbles, when hurried along by 

 the violence of the stream, are thrown 

 against every obstacle lying in their way, 

 and thus a power of attrition is acquired, 

 capable of wearing through the hardest si- 

 licious stones, on which water alone could 

 make no impression. LYELL Geology, ch. 

 14, p. 204. (A., 1854.) 



1296. FORCE, ORIGIN AND EXTEN- 

 SION OF IDEA OF Power an Essential Ele- 

 ment of Causation. When, however, we not 

 only look at bodies in motion, but try to 

 resist their motion by an exertion of our 

 own, or use a similar exertion in giving mo- 

 tion to a body at rest, we are led, by our 

 own sense of effort in making it, to an en- 

 tirely new conception, that of force ; and no 

 advance in the philosophy of science has 

 been greater than that which has of late 

 years extended the notion of force, from 

 the agency which produces or resists the 

 motion of masses, to the agencies which 

 are concerned in producing the molecular 

 changes which we refer to heat, light, elec- 

 tricity, magnetism, etc. The man -of science 

 of the present day is thus enabled to attach 

 a distinct idea to that efficient causation 

 which logicians have continually denied, but 

 which the common sense of mankind has 

 universally recognized. When the cause of 

 any event is spoken of, in common parlance, 

 we certainly attach to the term the idea of 

 power, at the same time that we include the 

 notion of the conditions under which that 

 power operates; and this view of the case 

 can be shown to be scientifically correct. 

 CARPENTER Mental Physiology, ch. 20, p. 

 693. (A., 1900.) 



1297. FORCE, THE DIRECTION OF 



Importance of Initiative Early Metal- 

 lurgy Heat-engines. When a savage sof- 

 tened or melted a lump of copper in a blaze, 

 his act was one of direction rather than of 

 execution; to have warmed the metal by 

 repeated blows would have been a toilsome 

 and unrewarded task; while to place the 

 copper in the flame and duly to remove it 



