Sept. 21, 1S83/1 



» KNO\A/LEDGE ♦ 



179 



gave the superficial area of the left-hand group as 

 702,940,200 square miles, and that of the right-hand one 

 1,074,370,000 square miles, or, in all, 1,837,310,200 square 

 miles of the sun's surface, as involved in this stupendous 

 disturbance alone ! It could be seen with the naked eye 

 when defended by a darkened or smoked glass. There 

 were other spots on the sun's disc at the time. Careful 

 study of the spots under the most favourable definitions 

 will reveal certain striking features. The umbrw, under 

 ordinary circumstances, seem to be black ; but the student 

 who has the opportunity of watching a partial solar eclipse, 

 or a transit of Mercury, will at once be struck with the 

 extreme blackness of the moon's limb or of the planet, 

 as contrasted with the (now, by contrast) brown hue of 

 the spots. A distinctly brown, and even orange tinge 

 may often be seen in the images of spots projected on 

 to a sheet of cardboard, in the manner described above. 

 Attentive study of the penumbra will reveal a kind 

 of fimbriated or fringed appearance in it ; and it will be 

 further noticed to be darkest at its outer edge, and seem- 

 ingly to get lighter as it approaches the umbra. Returning 

 now to the limb, or edi;e of the sun, which, as we have pre- 

 viously said, will be perceived to be notably darker than 

 the centre of his disc, we shall find the shading diversified 

 by curious and often rather complicated streaks of light. 

 These are called " facula;," and are most numerous and con- 

 spicuous about spots which are close to the limb, or where 

 such spots are aliout to break out. We have sometimes 

 traced facuhe for some considerable distance on to the 

 brighter part of the sun's disc ; but, as a rule, they are 

 only seen near the limb. The sketch which follows 

 represents a group of faculfe which was visible on the 

 morning of Aug. 25, at 9 h. 40 min. : — ■ 



Fig-. 3.— Facul;i^ on Sun's limb, Aug. 25, 1883, 9.40 a.m. 



It was drawn on the paper on to which the image of the 

 sun was projected, in the manner previously described. 

 The fourth piece of solar detail of which we need here 

 speak is tlie mottling or graining of liis surface. This is 

 best caught by shifting the telescope a little, so as to make 

 the sun's imago move about in the field. If this be done, 

 the eye will soon receive the impression of a roughness or 

 grain upon the sun's face, akin to that of a piece of magni- 

 fied loaf-sugar. In large instruments this is seen under the 

 best definition to consist of markings which have, not 



unaptly, been compared to rice grains, but its resolution 

 into these appearances is whoUy beyond our instrumental 

 power. 



Such are the leading features observable on the surface 

 of the sun with the means at our disposal. Mutatis mu- 

 tandis, we may say, as we did concerning the moon, that we 

 are not writing a heliogi-aphical treatise ; and hence, for 

 their interpretation, must refer the reader to " The Sun," 

 by the Editor of this Journal, or to the volume of the 

 " International Scientific Series," bearing the same title, 

 by Professor Young. We have simply essayed — not, we 

 trust, wholly without success — to indicate what may be seen 

 upon the sun in a three-inch telescope. By the aid of 

 Browning's star spectroscope, with a very narrow slit, the 

 spectra of prominences (those huge uprushes of hydrogen 

 gas known as the " red flames " which are seen during a 

 total solar eclipse) may often be detected on the sun's limb, 

 even in a telescope of the size of that whose use is pre- 

 supposed ; but the mention of the fact must sufiice here. 



THE FISHERIES EXHIBITIOX. 



By John Ernest Ady. 



AMONGST the numerous exhibits which bear upon our 

 subject, there are perhaps few which call for more 

 attention than those concerned with the supply of water 

 for domestic use. 



On the left-hand side of the passage leading to the 

 aquarium gallery, a remarkable filter is being exhibited by 

 Mr. P. A. Maignen, called the " Filtre Eapide." For sim- 

 plicity in design and efficient working qualities, this filter 

 deserves some notice in these columns, especially as a short 

 description may bring a very useful article within easy 

 reach of many of our readers. In Fig. 16, two sectional 

 diagrams are given of this apparatus. The explanation 

 under the figures will suffice to convey an idea of their 

 structure, which shows that the filter itself consists of 

 movable pieces, which can thus be thoroughly cleansed and 

 replaced with very little trouble, and at a merely nominal 

 expense ; the cleansing process, moreover, need not be 

 repeated oftener than once during the course of about 

 three months. 



'^rr^'z 



-::3 



Fig. 10. — Shxriox.iL Views OF MAUNtx^ ■■ I'li.ritE Kapide." — A, 

 reservoir for the filtered water ; B, the filter ease, which is re- 

 movable ; D, conical sac of asbestos cloth tied over the filtering 

 frame, which consists of a funnel-shape jierforated piece with outlet, 

 W, and aSrating pipe, C. On the outside of the asbestos cloth a 

 charge of powdered " carbo-calcis " is deposited, by being mixed 

 with tlio first water run into the filter. This forms a layer on the 

 clotli through wliich all subsequent water must pass and be purified. 

 E, scrroii for protecting the filtering medium. The figure to the 

 right-hand side is a different form of the same apparatus. 



In the majority of filters now used, two types of con- 

 struction have invariably been followed, both of which are 



