Aug. 8, 1884.] 



♦ KNOWLEDGE ♦ 



109 



as likely to adopt the new views as to retain their confidence 

 in the ruodern system of astronomy. 



I would not have it undeistood that the present series of 

 papers is in any way intended as an answer to the para- 

 doxists — whether of the honest or of the dishonest school. 

 To enter into controversy with these writers would be not 

 only a foolish, but a wrong thing to do. It would imply 

 that modern astronomy, and — which is more important — 

 the professoi-a of modern astronomy, require to be defended. 

 The task would also be necessarily a vain one, sinee the 

 honest paradoxist cannot, and the dishonest paradoxist will 

 not see the futility of their ai-guments. Nor does either 

 class, indeed, deserve to be answered, since even the honest 

 paradoxist — though otherwise to be commiserated — yet 

 merits condemnation for professing to teach matters which 

 he has not mastered, and so leading others astray. 



It is for the benefit of those who really wish to know 

 something of the grounds on which the modern system of 

 astronomy rests, that I pen these papers. I wish to indi- 

 cate the way in which the various parts of the evidence 

 dovetail into each other, and to show how observed facts 

 are accounted for, not merely in a general way, but in 

 measure and quantity — the only true test of a theory. 

 Lastly, I may find occasion in passing to notice some of 

 those absurd hypotheses which now, as at any time tince 

 Newton's day, find supporters and believei's. 



A large part of the evidence I shall present to the reader 

 is such as he can himself abundantly verify ; but necessarily, 

 a very large part remains which has to be taken on trust. 

 I cannot call upon readers to take sail for the southern 

 hemisphere and make such and such measurements or ob- 

 servations. I cannot ask them to devote a whole life to 

 the study of practical astronomy, that they may be able to 

 make those exact and delicate instrumental observations on 

 which modern astronomy in large part depends. Nor can 

 I insist that every one of my readers shall master the 

 higher branches of mathematics so thoroughly that, if need 

 were, he could follow Adams and Leverrier through all the 

 intricate calculations by which they have extended our 

 knowledge of the structure of the universe. 



On many points, therefore, I shall have to confine myself 

 to giving as clear aud exact a statement of what is or of 

 what has been done as I can, without being able to give 

 evidence which can be tested, or of showing in all cases how 

 such and such facts have been determined. In all such 

 cases I shall have to claim the reader's trust, to ask hiiu to 

 believe in the exactness and honesty of modern astronomical 

 work. Now so much has been heard from the paradoxists 

 of the cliquism of astronomers, of their determination to 

 uphold a false system at all costs, and of other such matters, 

 that many have been led (absurd as it may seem), to feel 

 doubts as to the bare honesty of the professors of modern 

 astronomy. To all such I would say, judge astronomers in 

 this respect as you would judge other men if you had occa- 

 sion to question their honesty of purpose. Ask whether it 

 is for the interest of astronomers to uphold a false system. 

 Consider whether it is in accordance with what we know 

 of human nature, that they should combine to laud the 

 names of a Newton, a Copernicus, or a Kepler, in defiance 

 of truth and justice. 



On the first point it is easy to find an answer. The 

 whole system of modern astronomy depends for support on 

 the exactness with which it records or anticipates the 

 celestial movements. Certain processes are applied for this 

 purpose, which satisfactorily accomplish all that is rei:|uired. 

 These processes might be continued without change, though 

 the whole system on which they were founded should be 

 abandoned. Thus the si.gle end and aim of practical 

 astronomy, that purpose for which our observatories are 



founded, and our astronomical stafi" salaried, could be ac- 

 complished as well as at present, though Newton wert^ pro- 

 claimed a charlatan, and Copernicus a cheat. So far then 

 ■we see nothing to lead to the suppression of the truth, if 

 the truth really required the overthrow of modern theories. 



On the second point we can found a yet stronger claini 

 for the confidence of our readers in the work of astronomers. 

 Newton and Copernicus are long since dead. They can 

 extend no patronage to the astronomer in return for the 

 respect and admiration with which he speaks of them. To 

 suppose that Aii-y, or the Herschels, Adams, Leverrier, or 

 Hind, would praise Newton for a theory which they knew 

 to be false, is not only to give them very little credit for 

 honesty, it is to assert that they are blind to their own 

 interest. If an unknown man, indeed, were to assert that 

 Newton and Kepler were mistaken in their theories, we 

 should, of course, pay no attention. But if Mr. Hind, for 

 example, were to announce such a belief, he would be heard 

 with respectful attention, .ind if (to conceive the incon- 

 ceivable) he could establish the justice of his view, he 

 would immediately rank high above the highest in the long 

 list of eminent astronomers. So of any of the others 1 

 have named. On this second ground, therefore — that it is 

 not in accordance with what is known of human nature 

 for any man, still less for a set of men, to praise another 

 (long since dead) for false theories, when he himself might 

 acquire like or higher praise by overthrowing them — I con- 

 fidently claim from my readers the acceptance of the 

 results of all those observations, measurements, or experi- 

 ments which have been made by modern astronomers. 



The method I propose to adopt in the forthcoming pages 

 is the same that I employed in the first chapter of my 

 treatise on Saturn, and is in great part new. 1 shall show 

 how a person wholly unacquainted with modern astronomy, 

 might have the true relations of the earth exhibited to 

 him in a series of simple observations. The particular 

 order I shall select for presenting those relations might be 

 departed from, since the subject is one which admits of a 

 considerable variety of treatment. Other methods have, 

 indeed, suggested themselves to me, but I believe that, on 

 the whole, the one I have adopted is that best calculated to 

 present the subject in a clear and satisfactory manner^ 

 within such limits as are hei-e available. 



{To he continued.) 



THE ELECTRO-MAGNET. 



Bt W. Slingo. 



(Continued from p. 69.) 



I All anxious to keep clear of formula as far as I can^ 

 but at the same time to impart as much information 

 as possible concerning the electro-magnet and the principles 

 governing its structure. The two very simple equations 

 at the end of the previous article may facilitate matters 

 very materially. It was shown that with a coil of the 

 relatively thick wire a current was produced, having a 

 a strength of 1 -3 amperes, and that when the diameter of 

 the wire was reduced to one half, so as to get twice the 

 number of turns, the current strength was reduced to -i 

 ampere, or less than one-third of that attainable with the 

 thicker wire. One of the laws of electro-magnetism is 

 that the strength of an electro-magnet is proportional to 

 the strength of the current. This is only true when the 

 number of tnrns is the same, because each time the current 

 circulates round the iron core it exerts its electro- 

 magnetic effect. This law has therefore to be taken in 



