Jl'LY, 191< 



KXO\VLF,DGE. 



267 



perceptible to the unaided eye. It was ver.\- unfavourably 

 placed on the 24th, when hardly anything could be made 

 oui in it through the telescope, except the colour, which 

 was yellowish, and the general phase, the disc being 

 then discerned to be approximately fifty per cent, illumined. 

 The disc was at all times very small in apparent di- 

 mensions, and at no time could a power to exceed eight-four 

 diameters be employed for studying it, while fifty-six was 

 nearly always preferable. On the 27th it was about 0-4 

 illuminated, and the apparent diameter, according to The 

 Nautical Almanac. \va.s 7" -16. On March 30th, the planet 

 was viewed to much better advantages, as it was " picked up " 

 in strong twilight by the aid of the circles. The crescent form 

 was nicely apparent, it on that date consisting of about 0-35 

 of the entire disc. The colour of the planet was golden yellow, 

 although this might have been somewhat intensified by the 

 low position of the body. The general color of the illumined 

 portion of the disc was found to shade oft" gr.adually back from 

 the terminator, it being lighter in the neighbourhood of that 

 region than elsewhere. This shading was the only topographi- 

 cal feature visible on the planet (through my instrument at 

 least), at the present elongation. 



The Snn was observed on 1912. April Jrd. not under very 

 favourable conditions, however, but as far as could be made 

 out with the three-inch telescope, its disc was perfectly free 

 from spots and all other phenomena. 



FREDERICK C. LEONARD, 



President S.P.A., M.B.A.A. 

 l.iiH. Madison Park, 



Chicago, Illinois, U.S.A. 



HOW TO MAKE STEREOSCOPIC STAR CHARTS. 

 To the Editors of " Knowledge." 



Sirs, — Referring to the article by Mr. A. H. Stuart in June 

 " Knowledge." " How to make Stereoscopic Star Charts," 

 I should be glad to know- when the .American firm he speaks 

 of placed upon the market a series of Stereoscopic Star 

 Charts. To the best of my belief the first stereoscopic views 

 of the stars were those published by me in my " Road Book 

 to the Stars," February, 1905. These were followed by " Six 

 Stereograms of the Sun and Stars," which I had the honour 

 of exhibiting at the Royal Society's Conversazione, in May, 

 1905, and followed again in November, 1905, by my ''Stereo- 

 scopic Star Charts and Spectroscopic Key Maps," which I also 

 exhibited at the rooms of the Royal Society and Royal 

 Astronomical Society. As far as I could then gather no 

 one had ever seen or heard of anything of the kind before. 

 All these were not only printed and published by Messrs. 

 King. Sell & Olding, Ltd., but were also reproduced as very 

 beautiful transparencies and lantern slides by Messrs. Flatters 

 and Garnett, Ltd. .-Vs regards this country I own the copy- 

 right, but not for America. 



In The English Mechanic, of October 27th, 1911, Mr. 

 A. H. Stuart. B.Sc, F.R..A.S., published a Stereoscopic Star 

 Chart, which is obviously a copy of my Stereoscopic Star 

 Chart, No. 12, with the small stars blocked out. The stars, 

 as in my chart, are white on a black ground. Presumably, 

 this was taken from the American Stereoscopic Star Charts 

 he refers to. and if so it can easily be understood why " very 

 few of the slides have found their way into England." 



The Star Stereogram Mr. Stuart gives in June " Know- 

 ledge " is doubtless quite original, but it is calculated to 



convey the very erroneous idea that the distance of a star 

 can be inferred from its magnitude. 



It goes without saying that the correctness of the result in my 

 Stereoscopic Star Charts depends upon the parallaxes upon 

 which they are based being right. I had to do the best I 

 could with the material I could collect. In twenty or thirty 

 years time much more reliable data will be available, and then 

 Stereoscopic Star Charts made by my method will be very 

 valuable. Therefore, it is certainly desirable that others 

 should be able to use it, when there are plenty of good 

 parallaxes and proper motions. 



TEN.n. '"• E- HEATH, F.R.A.S. 



SEA SICKNESS. 

 To the Editors of " Knowledge." 



Sirs, — Without entering into a deep treatise on the subject 

 I think I might interest some of your readers by mentioning 

 a factor which is very little thought about, the different 

 rhythm in the waves. 



Many people are surprised to find themselves experiencing 

 rough weather without the least sign of sickness, while at times 

 previous they have been dreadfully sick while the weather 

 was nothing like as rough. 



Now although that can partly be accounted for by the 

 person being in different states of health, nerves and .system 

 generally, nevertheless it is also due to the dift'erence in the 

 rough weather, the diftcrent rhythm of the waves. For 

 instance, I have been in the Kay of Biscay in apparently calm 

 sea and have been fearfully sick, because the wa\es were 

 exceptionally long and not high (a wave is measured from 

 crest to crest) — what we call a swell. .And I have been in 

 very rough weather and not sick, because the waves were 

 high but not long, and the motion of the boat, consequently, 

 was a quick rise and fall, quite the rever.se to the previous. 



That is only a broad example to illustrate my meaning. 

 There is a lot more in it than that. It depends also on tlie 

 regularity or irregularity of the rise and fall, the height and the 

 speed of the rising and falling, and. the most important thing 

 of all, the length of time after the ship has descended before it 

 starts to rise again, which may be from a fraction of a second 

 to two or three. I have noticed that certain people are 

 specially sensitive to certain conditions of the sea or rhythm. 



Birkenhead. 



C. POTTER. 



THE FACE OF THIC SKV. 

 To the Editors of " Knowledge." 



Sirs, — I am glad indeed to see that the " Face of the Sky ' 

 is now a month in advance of issue. 



The want of that was the principal reason why I lin the 

 Colonies) gave up your journal some time ago. If Dr. 

 Crommelin would also use his remaining space to give a 

 summary of the results attained by the observatories of the 

 world, public and private, as regards observation of the planets 

 during, sav. the last decade, it would, I think, be a great help 

 to amateurs. 



Many amateurs have only more or less ancient history to 

 refer to, which, considering the improved instruments of these 

 days, would perhaps be better consigned, in a great measure, 

 to oblivion. 



\'ERN0N. B.C.. M. Inst. C.E. 



Canada. 



oup:ries. 



Readers are invited to send in Questions and to ansic'cr the Queries which are printed lure. 



7. INSECT ANATOM\'.— I am desirous of studying 

 the Anatomy (Internal! of the Hymenoptera aculeata, and not 

 having time during summer, w.ould like to know of any method 

 of preserving insects for this purpose ? 



H. W. 



I.uddenden. 



8. LIGHTNING. — What is the diameter of the main 

 stem of forked lightning (n) between two clouds, ib) between 

 cloud and earth ? does the diameter vary much ? what condi- 

 tions such variation ? yy >^ p 



Upper Norwood. 



