278 



KNOWLEDGE 



[December 2, 1895. 



waterfalls are of very frequent occurrence, I should think 

 the effect would be noticeable. Is it not probable that 

 Norway, for instance, would be appreciably colder, were 

 it not for its thousands of waterfalls ? 



Yours faithfully, 

 Boldmere Road, Erdington. Alfred J. Johnson. 



THE PrZZLE OF '^ti." 

 To the Editor of Knowledge. 



Sib,— It is easy to see that the solution of this problem 

 necessitates the condition that A + C + E = B + D-i-F, and 

 that one of these groups must sum 13. 

 Then in the numbers 1 to 12 there 

 are only eight groups of three numbers 

 each which fulfil this condition ; they 

 are as follows :— 10, 2, 1—9, 3, 1— 



3, 2-8, 4, 1—7, 4, 2—7, 5, 1— 

 6, 5, 2—6, 4, 3. 



Un Vieil Etudl^nt. 



To the Editor of Knowledge. 



Sir, — Referring to the problem in your last number, I 

 find that — 



(1) The numbers in the hexagon must comprise the 

 number 1 , since the sum of the next six lowest numbers is 

 greater than 26. 



(2) That the remainder, 25, may be gained either from 

 3, 4, 5, 6, 7, or from 2, 4, 5, 6, 8. 



(3) That the latter must be taken, because 3 + 11 + 12 

 are required for the angles of one of the triangles. 



Hence a little consideration leads to the following 

 solution : — 



26-(12 + ll) = l + 2 

 26-(ll+ 3) = 4 + 8 

 26- (12 + 3)= 5 + 6 



-(10 + 9)=6 + l 

 .( 9+7) = 2 + 8 

 -(10 + 7)=5 + 4 



•J. Willis, Ph.D. 



It 



To the Editor of Knowledge. 



Sir, — I have found one solution of the above puzzle, 

 is thus : — With regard to the modus of 

 solution it is simple. The S in A P of 

 figures 1 to 12 is 78, the outer ring twice 

 the inner. Take the last six numbers, 

 this gives five too many ; exchange 5 

 for 10, and place the numbers in outer 

 angles. Adjust the inner ones in alter- 

 nate angles round, 4 next 3, and on to 6. 



[Of the solutions sent in by your three correspondents, 

 I note that two — " T " and " J. Willis " — proceed on the 

 principles, first, that the outer ring shall be double the 

 inner ring, and, second, that the number in each outer 

 angle shall equal the sum of the two numbers directly 

 opposite ; while " Un Vieil Etudiant " proceeds on the 

 principle that the inner ring shall be double the outer 

 ring, which necessitates the giving up of the second con- 

 dition. Both solutions seem good, though they are not 

 only different, but different in results. — I. G. Ouseley.] 



THE DARK HEMISPHERE OP VENUS. 



To the Editor of Knowledge. 



Sir, — In connection with the letter by M. Antoniadi, 



which appears in the November number of Knowledge, I 



may perhaps be permitted to refer him to one of my own, 



on page 135 of your XVIIth Volume. 



Uckfield. William Noble. 



PHOTOGKAPHS OF NEBULE. 

 To the Editor of Knowledge. 



Sir, — The stereoscopic method for examining stellar 

 photographs, which was referred to by Mr. E. Holm 33 in 

 the November number of Knowledge, was tried some three 

 years ago by Mr. W. Crookes, F.Pi.S., with the object 

 of detecting stellar parallax ; but the original negatives 

 should be used for such purposes, because the quantities 

 to be dealt with would be very small. 



I have examined many stellar negatives taken at 

 different periods in duplicate, and have also examined 

 many thousands of the stars upon them by superposition 

 of the plates, but have not found any indication of dis- 

 placements of the stellar images due to irregular contraction 

 of the gelatine films. 



Those who may engage in the examination of the stellar 

 photographs published in Knowledge should be careful in 

 distinguishing between instrumental distortion of the 

 images of the stars, and the appearances caused by the 

 overlapping of the photo-images of double and multiple 

 stars ; and it would further the real useful work that may 

 be done in utilizing the photographs, if some simple 

 experiments and tests were made by the researchers 

 themselves before too readily yielding to the impulse of 

 writing — suggesting doubts and diificulties, many of which 

 they would soon find to be imigniiry only. When a real 

 difficulty appeared, then the enlarged positives-on-glass, 

 or the original negatives, could be referred to, or another 

 photograph taken, and in this way the difficulty removed. 



Crowborough. Isaac Roberts. 



[The readers may here be reminded of the care which 

 Dr. Roberts always takes to provide the co-ordinatej of at 

 least four fiducial stars on each pla'.e. The fiducial 

 stars themselves are marked by minute ink dots, thus ; — 

 (•).(••). (•••), ( ::)-]-Ed. 



XoTE.— The concluding portion of IVIr. Mauuder's ai'ticle, entitled 

 ■' Wh.at is a Nebula?" (the first part of which appeared iu the 

 Xorember number of Ksowledgb). will be published in tlie January 



NEW STARS. 



By Dr. A. Beester, Junr. 



IF my suggestion in the November number of Know- 

 ledge be accepted, and the periodical luminous 

 phenomena of the sun and the red variables can 

 be explained by the periodical dispersion of cloudy 

 matter R by heat due to a new combination of gaseous 

 molecules A and B, " new stars " need no other explanation. 

 In their sudden upblazing and gradual fading away we see 

 once more the sudden evaporation and gradual reappearance 

 of dark condensed matter shutting off the light from the 

 still glowing interior of the star, and in their strong bright 

 lines we see a vigorous luminescence, as a testimony to the 

 greatness of the chemical force that was needed for a work 

 so enormous as the dispersion of a dark crust, perhaps 

 many centuries old. A work so gigantic is not likely to be 

 practicable at once. It will proceed gradually with intervals, 

 and so cause the new star to show its well-known 

 fluctuations. 



As now under the never-ceasing loss of the star's heat 

 by radiation the vaporized crust condenses again, and so 



