248 



• KNOWLEDGE ♦ 



[Oct. 19, 1883, 



pains, as it presented a beautiful view, beiug covered with groups 

 of spots all over the zone in which they appear. 



I see by the daily papers that an unusual " blueness " was 

 observed on the orb, on the same day, [?] at Panama and Colombo. 

 It seems plausible to consider that our gi'eat " variable star" has 

 reached a minimum of light and a maximum of disturbed surface. 

 T. P. B., Lieut. K.A., F.R.A.S. 



GREAT SUN-SPOTS. 



[963] — I enclose a rough drawing of the sun-spot de.'Jcribed by 

 " Excelsior " [943], made with a terrestrial telescope of 2j-in. 

 aperture, on Sept. 16. It was visible to the naked eye as a black 

 spot to the right of, and below, the sun's centre. As far as I could 

 judge (being unprovided with means for exact measurement), it 

 was about Ij in. or IJ in. in length. There were no "bridges" 

 visible, but there were signs of their formation in the left-hand 

 spot. There were bright facula; to the right of the spot. 



YlGNOLES. 



^^%h. 



P.S. — How is it that the left-hand is the eastern Umb of the sun ? 

 I always thought the sun rotated from W. to E., in which case 

 would not the left hand be west ? Could you kindly explain the 

 mystery ? 



[When a man faces you would you not say that his right limbs 

 were to the left as you view him ? — R. P.] 



■" [964] — The most astonishing change has taken place on the 

 sun's sui-face since Saturday last. On that day the highest power 

 at my disposal could reveal but seventeen spots of size enough to 

 exhibit detail. The sun's disc was hidden by clouds and fog till 

 this morning, when, on turning my telescope (3-in. DoUond) on the 

 sun, I found the disc was covered with spots from limb to limb. I 

 could get but transitory glimpses owing to the clouds, but I 

 managed to obtain rough sketches, of which I send you copies, as 



Appearance of Sun, Oct. 10, 1883 (Power, 40). 



I think the complex construction of the group marked A in the 

 sketch might interest you. In this spot, which had but one 

 penumbra, I counted no less than twenty-three nuclei. I noticed 

 that the " granules " were exceptionally well brought out. Is this 

 the effect of fog ? The time was too short and the sun's image too 

 faint to measure the spots by projection, so the dimensions are 

 guess-work. However, I think I am justified in saying that there 

 ■were three or more spots of 2' or over in diameter. The most 

 northerly of the three huge spots has a very curiously spiral 

 appearance. It looks like two whirlpools, whirling opposite ways 



and joined together. My sketch of it was unfinished, owing to 

 clouds, but I hope to see it to-morrow. 



Group A.— Wednesday, Oct. 10, 1883, 3.30 p.m. 

 (Telescope, 3-in. aperture; Power, 80). 



What is the position of the solar axis as seen from the earth at 

 the different seasons of the year ? Not knowing this, I cannot even 

 approximately record their position from day to day. Then what 

 means are there of ascertaining if the equator of one's scale 

 coincides more or less with the plane of the ecliptic ? This, of 

 course, changes the aspect of the spots as seen morning and 

 evening. Tigxoles. 



[To these questions a reply shortly, with suitable illustrations. — 

 E. P.] 



MOON'S SURFACE. 



[965] — Some time ago, in Vol. I., I think, several methods were 

 given in Knowledge for producing a surface similar to that of the 

 moon. In the course of my work to-day, I came across a very 

 pretty illustration. By trade I am an electro-plater, and I had been 

 " throwing down " some old silver solution, and had got my silver 

 chloride precipitate settled at the bottom. After washing and fil- 

 tering, I had put it, in a pasty state, over a good strong gas-stove. 

 The temperature was high, and as the water began to boil it all 

 spirted up through the paste, and some splendid volcanoes were pro- 

 duced. With the steam that issued out of them, the more liquid 

 paste also rose, and flowing out of the mouths of the tiny craters, 

 and gradually drying, made those ridges or ranges of mountains 

 which one sees in the moon. In one place there was a most beau- 

 tiful " Copernicus," which was formed thus : — The steam out of one 

 crater kept on blowing thick babbles, which, bursting, formed a 

 ridge all round the interior of the crater. In another place I had 

 my " Tycho." The stuff gradually drying, cracked in several places. 

 I poked a thin stick down one of the craters, and when I pulled it 

 up the more liquid stuff from below came up also, and filled all the 

 fissures, making the thing look very real. 



I should think that the same thing done with plaster woiJd be 

 very useful, and would be more like the real thing than throwing 

 sand on to it. Silvebsmith. 



SMALL WHEELS FOR TRICYCLES. 



[966] — Some of my correspondents tell me that they should be 

 glad to try tricycles with smaller wheels, but makers tell them it 

 is impossible to make front-steerers with vertical pedalling, so as 

 to keep the heels of the riders clear of the axles, without putting 

 the riders so far forward that a considerable weight shall be thrown 

 on to the front steering wheel. 



This is a mistake. Messrs. Singers have recently made to my 

 instructions an "Apollo Sociable" with 40-in. wheels. With the 

 saddles almost over the pedals the machine is so well balanced that 

 the front wheel can be easily lifted by a sharp pressure of one foot 

 by a single rider when both are seated, and yet the heels of the 

 riders are clear of the axles by about liin. 



John Beowning, Chairman of the London Tricycle Club. 



TRICYCLE WHEELS. 



[9G7] — A few days ago I had Knowledge sent to me, and I much 

 regret I have not seen it before. I can only say in future I shall 

 read it regularly. As I am writing a treatise on the theoretical 

 and practical construction of the tricycle, which I hope to be able 

 to publish before the next spring exhibition, I am much interested 

 in the letters of " Sigma " and others regarding the size of the 



