SCIENTIFIC SIDE-LIGHTS 



752 



operation leading to local styles. If these 

 women were moved far away, they carried 

 oftentimes these processes with them, and 

 plied the old trade upon such strange ma- 

 terials as they discovered in their new home. 

 MASON Woman's Share in Primitive Cul- 

 ture, eh. 3, p. 41. (A., 1894.) 



3723. WEAVING OF THE SPIDER 



Fluid Silk Hardening by Exposure to the 

 Air. Like the silk-moth's caterpillar, or the 

 mussel in the sea, which are also spinners 

 and weavers, Madame Spider's silk-secretion 

 exists within her body in a fluid state. It 

 is made and secreted by certain silk-forming 

 glands which end in the " spinnerets." These 

 last are conical projections placed near the 

 tail; and comparative anatomy seems to 

 teach us that the spinnerets really represent 

 much-altered limbs. Each of these organs 

 seems in its essential nature to be composed 

 of a multitude of fine tubes, opening at the 

 top of the spinneret. This, then, is the ap- 

 paratus wherewith our spider weaves. 



Let us see how the weaving is carried on. 

 The silk, while within the glands, exists in 

 a semifluid state; but when it is exposed 

 to the air it becomes dried, or of a more 

 tenacious consistency, and in this state is 

 susceptible of being drawn out into a fine 

 thread. Think for a moment what happens 

 to melted wax or glue. So long as the heat 

 is of sufficient amount either substance re- 

 mains fluid; but if we draw a little out of 

 the pot on a piece of stick, exposure to the 

 air hardens the wax or glue, and with a 

 little dexterity we can produce the melted 

 substance into a fine thread. This repre- 

 sents accurately enough how and why the 

 semifluid silk of the spider becomes a dry 

 thread when it is pressed out through the 

 fine tubes of the spinnerets. WILSON 

 Glimpses of Nature, ch. 6, p. 23. (Hum., 

 1892.) 



3724. WEIGHT BALANCED AGAINST 

 DISTURBING FORCE The Spider's Knowl- 

 edge of Mechanics. Practical acquaintance 

 with mechanical principles ... is some- 

 times shown by spiders when they find that 

 a widely spread web is not tightly enough 

 stretched, and as a consequence is to an 

 inconvenient extent swayed about by the 

 wind. Under such circumstances these ani- 

 mals have been observed to suspend to their 

 webs small stones or other heavy objects, 

 the weight of which serves to steady the 

 whole system. Gleditsch saw a spider so 

 circumstanced let itself down to the ground 

 by means of a thread, seize a small stone, 

 remount, and fasten the stone to the lower 

 part of its web, at a height sufficient to 

 enable animals and men to walk beneath it. 

 ROMANES Animal Intelligence, ch. 6, p. 

 220. (A., 1899.) 



3725. WEIGHT OF THE SUN Den- 

 sity One-fourth That of Earth Mass Not 

 Proportioned to Size. We now know that 

 the sun's average distance from the earth 

 is about 93,000,000 miles, and consequently 



that his diameter is about 865,000 miles. The 

 sun has been weighed against the earth and 

 found to contain a quantity of matter nearly 

 330,000 times as great, and comparing this 

 with his enormous bulk, it appears that his 

 mean density is only about one-fourth that 

 of the earth, or one and a quarter times 

 that of water in other words, the mass of 

 the sun is about one-fourth greater than 

 that of a globe of water of the same size. 

 YOUNG The Sun, int., p. 7. (A., 1898.) 



3726. WHEEL, THE, A PREHIS- 

 TORIC INVENTION The Primitive Farm- 

 cart War-chariots with Spoke-wheels in 

 Ancient Egypt Railway Wheels and Axles 

 Return to Primitive Type. The wheel-car- 

 riage, which is among the most important 

 machines ever contrived by man, must have 

 been invented in ages before history. To see 

 what constructive skill the leading nations 

 had already attained to in times we reckon 

 as of high antiquity, it is worth while to 

 examine closely the Egyptian war-chariots, 

 with their neatly-fitted and firmly-tired 

 spoke-wheels turning on their axles secured 

 by linchpins, while the body, pole, and 

 double harness show equal technical skill. 

 In looking for some hint as to how wheel- 

 carriages came to be invented, it is of little 

 use to judge from such high skilled work 

 as was turned out by these Egyptian chariot- 

 builders, or by the Roman carpentarii or 

 carriage-builders from whom our carpenters 

 inherit their name. But as often happens, 

 rude contrivances may be found which look 

 as tho they belonged to the early stages of 

 the invention. The plaustrum or farm-cart 

 of tLe ancient world in its rudest form had 

 for wheels two solid wooden drums near a 

 foot thick, and made from a tree-trunk cut 

 across, which drums or wheels did not turn 

 on the axle, but were fixed to it; the axle 

 was kept in place by wooden stops, or passed 

 through rings at the bottom of the cart, and 

 went round together with its pair of wheels, 

 as children's toy carts are made. It is curi- 

 ous to notice how, under changed conditions, 

 the builders of railway carriages have re- 

 turned to this early construction. 



In such countries as Portugal the old classic 

 bullock-cart on this principle is still to be 

 seen, and it has been reasonably guessed that 

 such carts tell the story how wheel-carriages 

 came to be invented. TYLOR Anthropology, 

 ch. 8, p. 198. (A., 1899.) 



3727. WHEELS FOR VEHICLES UN- 

 KNOWN IN AMERICA BEFORE COLUM- 

 BUS The Fly-wheel for Spindles and Drills. 

 There was nothing on the continent that 

 could be compared to a wheel, either for 

 carriage or for mechanical purposes, when 

 Columbus discovered America. The fly-wheel 

 was well known and widely distributed on 

 spindles and drills, but there were no wheel- 

 barrows, carts or carriages, no cranks, or 

 windlasses, or capstans. But the Alaskan 

 Indians, and perhaps others, used the par- 

 buckle, which combines the roller and the 



