48 



KNOWLEDGE. 



February, 1911. 



Dec. 16 ... 38—38 ... X.E. toS.W. Fog higher 

 ,. i: ... 34—40 ... X.E. to S.W. Fog on 



t^ip of inount.'iin.'; 

 „ IS ... 34—36 ... Ditto 



,. 19 ... 34—36 ... Wind X.E. to S.W No mists 

 „ 20 ... 28-36 ... Ditto 



„ 21 ... 31—40 ... Ditto 



., 22 ... 31 — 33 ... Snow from S.E. falling on 



foot hills 



Vou will see from tii.v .'jove that the high tides of December 

 may have something to Jo with weather here. 



While writing m,-: ' ask, .^re there what are known as half 

 tides anywhere ex . on Pacific Coast — what are known as a 

 long run in and a . .lort run out and a short run in and a long 

 run out ? 



Gl'X). DITCHAM. 



THE ETERN.AL RETURN. 

 Tu the Editors of " Knowledge. "' 



Sirs. — In a book by Mr. J, M. Kennedy, on the German 

 philosopher Niet^che, the following theory is promulgated by 

 the latter, the data being deri\ ed from the work of the great 

 French astronomer La Place ; and it appears that the same 

 theorj' was evolved independently by Blanqui, the famous 

 agitator, also Dr. Gustave Le Bon, and Heine, the German 

 poet, and is said to be found in Ancient Greek Philosophy. I 

 will endeavour to express it as succinctly as possible. 



" Time and space are infinite, but the sum total of the 

 forces in the Universe appears to be constant and determined. 

 It is impossible to conceive their diminution or increase. 

 There is therefore a sum of constant and determined forces not 

 infinite. If these forces could ever attain a position of balance 

 it would have already happened, as an infinity of time has 

 passed, and the world would be for ever immobile, as it cannot 

 be conceived that once attained such a state could alter. The 

 sum total of these forces will bring about in infinite time a 

 vast number of combinations, and produce some that have 

 already been realised, and therefore the entire series of 

 combinations that have existed. Universal evolution brings 

 about the same phases, and travels round in an immense circle 

 for all eternity, from which it follows that every identical 

 individual has already lived the same life an infinite number of 

 times and will continue to do so for ever." Dr. Le Bon 

 expresses it thus: "If it is the same elements of each world 

 which serve after its destruction to create a new one, it is easy 

 to understand that the same combinations, viz., the same 

 worlds inhabited by the same beings, may be repeated time 

 after time, the possible combinations being limited and time 

 unlimited." 



I write to ask is there any Haw in this reasoning, and if so 

 what is it ? This theory seems to me to pre-suppose that every 

 world is destro3'ed by collision with another before being 

 renewed, but as space is infinite it is difiicult to understand 

 why a dead world may not continue to travel for ever without 

 coming in contact with another. What ground is there for 

 thinking that the sum total of the forces in the Universe is 

 constant and determined ? In an infinity of space one would 

 suppose that these forces nuist per\ade infinite space, as 

 absolutely vacant space seems unthinkable. Wliat is the 

 opinion of scientists on the subject ? 



H. D. B.\K(■LA^■. 



PoDURA SCALi:s. 

 To flic Hilitors ((/"Knowledge." 



Sirs, — In reply to Mr. 1. L. Smith's correspondence it is 

 quite evident he has "blundered greatlv." 



It is not sufficient that his 1-4 objective, with cedar oil to 

 the cover glass, be coiuiected with the scale, in what Mr. 

 Smith believes to be optical contact, to obtain an aperture of 

 1-4, but that the cone of light which impinges upon the 

 scale shall also ha\e as large an angle. Xow this is 



impossible with scales simply mounted in air; the way Mr. 

 Smith has his mounted (what other medium does he suggest 

 is between the cover glass and the slip?) even supposing the 

 scale really was in actual contact with the cover all over — he 

 will understand I cannot possibly agree that this is so under 

 the circumstances appertaining — beneath the scale and above 

 the glass slip is — what? Air? Xow, even if using an oil 

 immersion condenser of 1'4 made homogeneous with cedar oil 

 to the slip, so soon as the cone of light had passed through 

 this, into the air space — however small — down would drop the 

 aperture to 1-0, as air cannot possibly convey a greater angle 

 than this between two parallel siu'faces. 



This fact is used as the standard or starting point of 

 refractive indices, and known as the "normal of air." If. 

 again, he had the scale mounted dry between two cover 

 glasses, as he says, truly this would make " confusion worse 

 confounded " ; in the first place it would simply throw his 

 condenser out of correction, as they are all corrected for a 

 certain thickness of slip, and should he have used a. dry 

 condenser he would have had two layers of air instead of one 

 for the light to pass through. It is quite evident he has 

 forgotten one of the principles of microscopic vision, and that 

 is, it is not the actual object he sees when looking through the 

 eyepiece, but simph- an image of that object formed some 

 distance up the tube of the microscope, and given an incident 

 air angle of I'O upon an object it would not matter if an 

 objective of 2-40 were immersed upon it — the resolving power 

 would be no greater than 1-0. Again, if, when looking down 

 the tube he thought he was getting 1-40 N..A., and which I 

 ha\ e showqi could not possibly be more than TO, he further 

 closed this aperture until only three quarters of that opening 

 was visible, he was actually getting much nearer '75 than T40. 

 an aperture not so great as a good dry ([uarter inch objective 

 would have given him as regards resolving power. The cover 

 glass idea might also be shown to be fallacious from the very 

 fact that such a small stratum of .air intervenes, apart from 

 condenser uncorrections. 



There is an axiom also which seems so often neglected, that 

 the visibility of very minute structure is proportional to the 

 difference between the refractive index of the object and the 

 medium in which it is immersed, — which I particularly tried to 

 emphasize in my previous letter — and that it is essential if 

 the whole aperture of an objective is to be utilized to mount 

 such minute structures in some medium other than air. As 

 this has never been done successfully (so far as I am aware) 

 with the Podura Scale he will be able to realize what I mean 

 when I say that " here, then, we make no advance upon the 

 very earliest methods." Until such a medium is found and 

 the scale successfully mounted, we are left with the only 

 alternative in contrast between the TO of air and the T5 of 

 the scale itself, a practicability of vision of -5 only. It may be 

 — I cannot say — that with vertical illumination a slightly greater 

 angle than TO might be obtained, but that, it seems to me, 

 would only help us with surface structure chiefly, and as this 

 runs one into the province of the optician's art, 1 cannot 

 venture to trespass. 



I ha\e not yet heard of a dry objecti\e which can give an 

 aperture of TO, and Mr. Smith's explanation of the "tilted 

 light to the object " in the microscope and the " moon it is 

 that revolves " are really too ab,struse for me. 



In conclusion, I nmst apologise for my photographs being 

 too small for good reproduction, but if Mr. Smith would allow 

 the Editor to forward me his address, I should be pleased to 

 send him an actual enlargement of them, which would allow 

 him a much clearer view, I feel sure, than he can have at 

 present of their purport. I am obliged for his open remarks 

 and candid reply, and would like respectfully to suggest this 

 little experiment for him to make : take a slide, say, of 

 Pleiirosignia or Amphiplcura. mounted in Realgar, and using 

 his T40 objective immersed upon it. also a good condenser of 

 T40 immersed to the under slide of slip. Xow when the 

 object is in focus and the light axial, take out the eyepiece and 

 measure the diameter pf light coming through the objective — 

 then, take away this slide and substitute the slide of Podura, 



