March 1, 1886.] 



KNO^VLEDGE ♦ 



155 



her present condition. It is otherwise with those prior 

 clianges by which the earth passed to the stage when she 

 was fit to be the abode of living creatures. We have 

 evidence, indeed, here also, but it is not so close at hand. 

 We have knowledge of the chemical and physical laws 

 involved in the problem, but the conditions under which 

 the processes then taking place proceeded were unlike 

 any under which we can now ex])eriment. So far as I 

 know, the problems suggested by the consideration of the 

 earth's fiery youth have not been as yet very closely dealt 

 with. Let us note some of the evidence, and some of the 

 points which may fairly be regarded as clear. 



In the first place, I think we are too apt to regard a 

 planet in its fiery youth as more uniform than the earth 

 is as we recognise it now. We find the idea common 

 that there would be a molten mass, with perhaps a 

 solid nucleus and a solid crust, and outside that, a 

 complex atmospheric envelope, high up in which would 

 be suspended immense layers of cloud, enshrouding the 

 real planet from outside view. These ideas seem as 

 likely to be erroneous as the common idea of -the 

 earth as enclosed in a uniform series of strata 

 before wind, rain, and storm cut her surface up into 

 mountains and valleys, hills and dales, ravines and 

 gorges. Probably the structure of the earth, when in 

 its fiery j'outh, was even very much more complex 

 than the contour of the earth's crust is now. All the 

 conditions favoured tremendous disturbances. The up- 

 heavals and down-sinkings of the crust, for instance, 

 would be very much more active then than now, 

 though it does not follow that the resulting inequalities 

 of level would be greater. Indeed, thej' would not be 

 nearly i-o great, for the simple reason that, whatever the 

 actual materials of the forming crust in those times, the 

 intense heat pervading it would suffice to render it too 

 unstable to be able to stand out to very great heights 

 above the mean level. But consider how rapidly it would 

 be changed by the subaerial forces which in those days 

 must have been at work. 



On our present earth we have an atmosphere of 

 oxygen and nitrogen producing a pressure of about 

 1.5 lb. to the square inch ; water is from time to time 

 added to it in the form of vapour raised by the sun's 

 heat from the sea, and it is this water, forming into 

 clouds, and jiouring down on the land, which leads to all 

 the denuding work of river, cataract, rain, snow, ice, 

 and glaciei'. In addition, there is the direct denuding 

 action of the air in wind and storm, the direct denuding 

 action of water as the waves of the sea pulsate on their 

 shore-lines. 



But such denuding forces can be absolutely as nothing 

 compared with the denuding forces which must have 

 been in operation when the earth was young. It is 

 certain that the oxygen and nitrogen now present in the 

 air are but a residuum of what was once there. But 

 besides these gases, now in due proportion for the 

 support of the earth's life, there were immense quan- 

 tities of carbonic acid gas, of sulphurous acid, sul- 

 phuretted hydrogen, chlorine, boracie acid, and other 

 destructive gases, some ready to assume the liquid form, 

 and so to be still more destructive. But there would also 

 be immense quantities — whole oceans one may say — of 

 water in the form of vapour, The pressure of that 

 primeval atmosphere would have been so great that the 

 waters of such oceans as would have existed then would 

 not have turned into steam save at a temperature so 

 far above the boiling point at the present atmospheric 

 pressure, that the surface of the ocean would actually 

 have glowed with inherent lustre. The water-vapour in 



the air would have been no such cool and pleasant vapour 

 as now exists in our air, but steam at high pressure and 

 intensely hot. The rains falling then would have been 

 torrents of hot water, impregnated with destructive 

 acids, and falling on intensely heated rocks, ready to 

 respond with intense rapidity to the destructive in- 

 fluences of those falling torrents, and of the dense, 

 complicated, and destructive atmosphere through which 

 they fell. We may be well assured that the changes 

 taking place in the aspect of the earth's surface during 

 that remote ]iart of her career were far more rapid than 

 those taking place now. — Newcastle Weeldij Chroiiirlr. 



ELECTRICITY AT HOME, 



By W. Slingo. 



exreriments with an electric machine. 



HE various parts of the electric machine 

 constructed on the plan detailed in mj 

 previous article require some little care 

 iu fitting together, and no pains should be 

 spared to ensure this being done as per- 

 fectly as possible. The great feature, of 

 course, is that the framewurk should form 

 a rigid structure, and one that is not likely to fail in any 

 part. If one of the uprights affords a firmer fit than the 

 other, it should be selected as the one which is to be 

 nearest the handle, and it is also this one that should be cut 

 across at the bearings (as in Fig. 3, p. 2.")). Presuming the 

 experimentalist is right-handed, so that he would be best 

 able to revolve the cylinder from him. that is, bj- moving 

 the handle in a similar direction to that taken by a watch- 

 hand, then the rubber and its .support should be placed 

 on the side of the base nearest him, and necessarilj- the 

 prime conductor should be placed on the opposite side. 



Before attempting the production of electricity, the 

 leather surface of the rubber should be coated with 

 amalgam. A small piece or strip of tin-foil should connect 

 the amalgam with the foil coating on the cylinder. The 

 silk rubber should be laid over the amalgam — a method 

 which will be found preferable to that of coating the 

 rubbing surface of the silk directly. 



It is essential for the production of any quantity of 

 electricity that there should be a. complete "circuity" or 

 path, for the electricity to travel ; from the rubber to the 

 prime conductor (by waj' of the moving cylinder) thence 

 back again directly or indirectly to the rubber.* More 

 often than not, the earth forms a part of the 

 " external " circuit (that portion external to the machine 

 itself). Should we wish to collect a charge, or secure a 

 series of flashes or sparks, we shall find that in most 

 cases it will best suit our convenience to connect either 

 the rubber or the prime conductor direct "to earth," or 

 to some other conductor connected therewith. In many 

 machines the rubber is made in electrical connection with 

 the framework, whereby a more or less perfect earth is 

 " made," bj' way of the table, floor, itc. 



By providing the rubber as well as the prime conductor 

 with an insulating support, we are, however, able to 

 secure a charge of positive or negative electricity at will. 



* It is to be observed here that, although I speak of the electri- 

 city travelling from the rubber to the prime conductor, I only use 

 this way of expressing the phenomenon in question because it is the 

 simplest mode of dealing with it. To enter into the question fully 

 would occupy several pages, and for those who are sufficiently 

 interested in the controversy there are many works on the subject 

 available. 



