May 12, 1882.] 



KNOWLEDGE 



593 



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ined and desptsed who is not in a 

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*' In knowledge, that 

 state of transition. . 

 than fixity of opinion."— JaroJoy. 



*' There is no harm in makinp a mistake, but great harm in making nc 

 me a man who makes no mistakes, and I will show vou a man wbi 

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" God's Orthodoxy is Truth."— CAdr^e^t EtngsUy. 



dBur Coirrsponbrnre Columns. 



SCIiEW-DRIVER TUBES. 

 [395] — 1 am afraid screws wouUl not take to my friend ifr. 

 Ellis's spiral tubes as kindly as ulcers do, even though it has since 

 been extended (as he doubtless knows) so that you can drill a hole 

 in a tooth — and the cheek behind it — in no time, with your foot, by 

 a drill at the end of a long spiral of that kind, which will -work 

 round any bead. But I do not write merely to say that, but to add 

 to my original mode and simple slate-pencil tube, that it may be 

 made of steel, and haye three slits, besides the opening in the 

 lower 2 inches of it, and the pieces may then be flattened and bent 

 outwards a little, enough to hold the largest scrcw-heail. A rin" 

 slipped oyer them will bring tlio fangs together, enough just to fit 

 smaller screws. Whether you see yonr screw or not, you can yery 

 soon feel if it is going crooked — the feeling is too enraging to 

 mistake for a moment. I obscrye (in both senses) your notice about 

 breyity of correspondence. Ei'M. Bec keit. 



COXSERVATIOX OF SOLAR ENERGY. 



[396J — I giye now in full Dr. Siemens's letter referred to at 

 p. 5GG last week, omitting only those references to Sir. Archibald, 

 to whom he was replying, which do not belong to the letter, re- 

 garded as a reply to my own reasoning in the Cornhill Maja:ine, 

 and at ])p. 5G5-5C0 of Knowledge. 



Dr. Siemens's letter, then, runs thus : — [Mr. Proctor] lias missed 

 the principal point of my argument concerning solar fan-action. I 

 showed pretty clearly I thought that solar gravitation would affect 

 the inflowing and the outflowing currents equally, and that centri- 

 fugal action must determine motion in the equatorial direction in a 

 space filled with matter. But, to put the problem into a mathe- 

 matical garb, let us consider the condition of two equal mas.scs, nip 

 and m,„ both at the radius li from the solar centre, the one opposite 

 either pole, and the other opposite the equatorial region. The 

 moment of grayitation of both these masses will be represented 



respectiycly by —^ and „, , and supposing both masses to be 



gaseous, aud of the same chemical composition and temperature, 

 they will represent equal volumes, say one cubic foot. 

 These conditions being granted, we may put — 

 gmp_'jm„ 

 R' R' ' 

 but the mass ui« is subject to another force, that produced by tan- 

 gential motion, which shall be represented by i-, and the centrifugal 



