234 



♦ KNOWLEDGE 



[August 1, 1888. 



nearly self-regulating in itself, as is shown by fig. 5, giving 

 the characteristic of the machine throughout a range of 

 37,000 watts. From tliis curve, it is clear that practically 



Fig. 3. — MoEDEY Altehnatok (Complete). 



the whole of tlie load — or say 600 larups — might safely be 

 turned off without danger to any remaining lamps, and that 

 probably a large proportion of the load, certainly 50 per 



ti: 



cent., could be turned ofl" without attracting notice on the 

 rest of the circuit. It is, therefore, not considered neces- 

 .sary or desirable, except under special circumstances, to 

 provide other than a simple hand regulation at the dynamo 



10 



Fic. 5. 



i^O Amperes 



for the purpose of controlling the potential difference. 

 Sudden and violent fluctuations of the lights are impossible 

 with this machine, and an occasional touch of the resistance 



regulator, as the load comes on or off, meets all practical 

 requirements. It is only in the case of machines whose 

 potential curve is a rapidly falling one that it is necessary 

 to resoi't to automatic control. There is no doubt that by 

 avoiding the use of additional apparatus of this sort the 

 chances of temporary interruption are reduced. By the 

 arrangement of the armature coils it is easy to obtain 

 various coaibinations if desired. This circumstance is made 

 use of for simplifying the measurement of the potential. 

 Instead of taking the reading across the terminals, which 

 would necessitate the use of an electrometer, or a very high 

 resistance voltmeter, an ordinary voltmeter, indicating to 

 100 or 150 volts, is jjlaced across one of the coils. The 

 machine is fitted with a special pair of voltmeter terminals 

 for this purpose. We understand that this dynamo of 

 50 to 60 horse-power — the first of its type — was successfully 

 built directly from the first design, without recourse to any 

 preliminary experiment. 



LOCKYER ON THE EARTH'S 

 MOVEMENTS.* 



A 8TEANGE PUZZLE. 



ESSES. MACMILLAX have never been 

 given to the publication of jocular scien- 

 tific books, or we might explain this work 

 as simply an elaborate jest. We cannot, 

 on the other hand, suppose that, though 

 published in all good faith as a serious 

 work by them, it was intended as a jest by 

 Mr. Lockyer, for he could not wilfully play off such a joke 

 on his good friends, the publishers of Xaturr. Yet he can- 

 not seriously regard this absurd production as a contribu- 

 tion to exact knowledge. It is true his "Elementary 

 Lessons in Astronomy" contained some marvellous blunders, 

 a few of the least preposterous of which were used in 

 astronomical examinations at Trinity College, Cambridge, 

 in the character of '•' awful examples," and in his " Primer 

 of Astronomy " he made some still odder mistakes — as, for 

 instance, in describing the stars which pass to the zenith of 

 London, which never rise or set at all, as rising and setting 

 " on a slant." But even this evidence that Mr. Lockyer 

 might not be able to recognise the full absurdity of what he 

 has brought out in the book before us does not prevent its 

 being a strange puzzle. For surely some friend, were it 

 only a well-taught schoolboy, might have been able to 

 explain to him that a book which, with an elaborate air of 

 condescension for the general reader, is utterly inaccurate, 

 confusing, and misleading, should not be sent to the 

 printers. 



It chances that we have had to conduct examinations of 

 students in astronomy, with the duty of determining who 

 had done best and best desei'ved certificates or other rewards. 

 In so doing we have sometimes felt appalled at the bewil- 

 derment of mind indicated in replies which related to 

 matters explained with ample clearness in the text-books 

 recommended by us, besides being most carefully, and as we 

 had hoped simply, explained by ourselves in preparatory 

 lectures. Well, we find again and again in Mr. Lockyer's 

 book passages recalling answers of this saddening kind — - 

 saddening, yet sometimes so ludicrous that we have had to 

 set down the papers we were examining to indulge in pro- 

 longed laughter at their absurdity. 



Of course the whole book is not absurd. We come across 



* " Outlines of Physiography. The Movements of the Earth.' 

 Jos. N. Lockyer. London : Maomillan & Co. 



By 



