116 



♦ KNOWLEDGE ♦ 



[Aug. 24, 1883. 



indeed, for the eye to appreciate its movement; yet if ita 

 course be, as it usually is, from the bottom to the top of 

 the glass frout of the tank, it will be marked out plainly 

 by the track left behind. Minute fragments of the base 

 are seen to adhere to the glass, which very soon contract 

 into a rounded form, and begin to grow tentacles round a 

 central mouth, and in time the minute creatures equal in 

 size the elder original. This increase by separation of 

 l)arts is analogous to the multiplication of plants by cuttings. 

 In both cases the colour remains unchanged ; whereas, in 

 the propagation of plants by seeds and of anemones by real 

 germs, the colour of the new production is arbitrary and 

 inconstant. 



Sometimes the irregular fragments, torn, as it were, from 

 the base, in contracting make two circular forms united 

 by a filament, and as the contraction continues, the uniting 

 link becomes a tine thread, and finally breaks, when two 

 individual anemones are formed. In this manner mon- 

 strosities probably have their origin ; the conuectiog thread 

 is not broken, and the two individuals grow up in contact, 

 or united together, and an individual appears with one 

 body and two disks. 



At the present moment, in tank No. 10, two very hand- 

 some anemones, a white and a bufl" dianthus, are attached 

 to the frout glass. They are nearly equal in siz", and 

 correspond fairly well in dimensions to Figs. 1 and 2 in 

 the preceding article (page 89), except that their bodies 

 are much shorter than in Fig. 2, which is possibly in con- 

 sequence of their position. 



A favourite practice with dianthus is to mount the side 

 of the tank as high as the edge of the water, and to remain 

 there protruding its column horizontally, and distending its 

 frilled disk so that the air and water are equally and 

 mutuallj' in contact with opposite parts of the base column 

 and disk. 



No British anemone is more hardy, or more readily 

 accommodates itself to confinement, than dianthus ; neither 

 is it what is termed a coy or a shy creature. It freely 

 expands and appears in flower during daylight. 



Still, it must be remembered that its natural habitat, 

 and that of all the sea anemones, is in the " dark caves of 

 ocean." 



Bearing this fact in mind, Mr. Gosse has very sagaciously 



Anemones are fed according to their appetite upon raw 

 beef, mutton, fish, oyster, mussel, cockle, limpet, ic. A 

 small fragment is held within reach of the feelers or placed 

 upon the disk. All the varieties which feed freely soon 

 degenerate in size and colour if they do not receive their 

 supplies regularly. 



An American dianthus — and in accordance with the 

 eternal fitness of things the biggest ever seen — is reported 

 upon and figured in the great American work edited by 

 J. W. Dana,* as follows : — Actinia Faumoieusis. From 

 the coral reefs Paumotu Archipelago. 



Smooth exterior, G in. thick at middle, above very 

 widely dilated (12 in.), tentacles numerous, covering the 

 larger part of the disk, yellowish-white, tipped with lake, 

 and marked with eight or nine transverse lines ; mouth but 

 little prominent (•/. Drayton). 



This species was truly magnificent when seen in the 

 water, the disk expanding at least a foot in diameter, 

 densely covered with tentacles, the margin undulating so 

 as to form numerous lobes, each of which had the 

 appearance of being a separate actinia, the whole resem- 

 bling a beautiful bouquet (J. P. Couthony). 



PRETTY 



PROOFS OF THE 

 ROTUNDITY. 



EARTH'S 



CHIEFLY FOR THE SEASIDE. 

 By Richard A. Proctor. 



(Co7itinued from page 102.) 



I HAVE received from a number of readers questions 

 relating to the determination of the actual amount of 

 depression of the earth's surface from a tangent line at any 

 point at given distances from the point of contact. In 

 particular some perplexity seems, strangely enough, to be 

 occasioned by statements as to the distance at which light- 

 houses of given heights have been seen from ships at sea. 



The actual depression of the earth's globular surface, 

 below a true tangent, is almost exactly 8 inches at a mile's 

 distance from the point of contact; four times this or 

 2 ft. 8 in. at two miles' distance ; nine times 8 in. or 6 feet 



pointed out the best way to make sure of seeing a tank of 

 anemones under the most favourable possible circumstances, 

 and at a time when all its occupants will be most likely to 

 display the full beauty of their gorgeous bloom. 



His advice to the benevolent reader is that he should 

 adopt Sir Garnet Wolseley's bean, siratagcme, so'success- 

 fnlly executed at Tel-el-Kebir against the Egyptians ; 

 which, of course, is to steal a night-march upon your 

 enemy and catch them napping. His words are : — " Visit 

 your tank with a candle an hour or two after nightfall." 



Some individuals of this species are voracious feeders ; 

 they swallow and partially digest bits of raw mutton and 

 fish once in two or three days, and grow wonderfully 

 larger and handsomer after each meal. The portions of 

 food eaten, so to speak, by anemones are retained for 

 several hours — sometimes days — and then vomited along 

 with true germs and egg-germs in many of the species. 



at three miles' distance ; and so on, — the depression in- 

 creasing as the square of the distance. Thus if PABO 

 (Fig. 11) is a part of the earth's surface, abc a tangent line 

 at P, rtA, JB, cO vertical lines to the surface PABO ; then 

 if Fa=ab=bc=l mile, Aa=8 in. ; B6 = 4Aa=2 ft. Sin.; 

 Cc=9Aa=C}it. &o. 



But the optical horizon line, tangent at P, has a slightly 

 curved course as Fb'c', owing to the refractive effects of the 

 atmosphere. Though this curvature Aa, Bi, Cc are each 

 reduced by about one-fifth so that 



Aa'=6|in.; B6'=4Aa'=2ft Ifin; Cc'=9Aa'=4 ft. 9|-in. 

 <tc., nearly enough. Refractive effect varies, sometimes 



* " Zoophytes," Vol. VII., p. 141. A fine copy of this really 

 splendid work, " Presented by the United States Congress to the 

 Government of Great Britain," can be consulted in the British 

 Museum Reading-room. 



