May 1, 1865.J 



SCIENCE-GOSSIP. 



117 



lime. This analysis, however, only indicates the 

 nltiuiatc elements, and not the mineral composition 

 of the rock ; and, to a certain extent, granites must 

 be regarded as mixtures of crystalline minerals in 

 various proportions. Thus it is also useful to ob- 

 serve that an average granite may be expected to 

 contain from two to three-fifth parts of crystals of 

 quartz or crystalline quartz, about the same, more or 

 less, of felspar, also partly crystalline and chiefly in 

 definite crystals, and the remainder (one-tenth part) of 

 mica. But the mica may form two or three-tenths and 

 tlic quartz three-fifths, or more, while the proportion 

 of felspai", as well as the particular composition of the 

 felspar, both vary extremely. Good ordinary granite 

 weighs 166t lb. the cubic foot, and the cubic yard as 

 nearly as possible two tons. Eourteen cubic feet to 

 the ton is the usual estimate. Its toughness or re- 

 sistance to crushing weights is very great, and is 

 believed to vary a great deal in different samples. 

 Eor practical purposes it is safe to assume that fresh 

 unweathered granite will bear any direct crushing 

 weight to which it can be exposed. Granite contains 

 a certain amount of water capable of being driven 

 off by continued exposure to a heat insufficient to 

 produce any other change. This quantity differs 

 much in different specimens, even of the same stone, 

 but it may be said to be represented by the " loss " 

 in the table of analysis. It averages, therefore, 

 about 0'8 per cent. Taken in its ordinary state, and 

 containing this quantity of water, it is still some- 

 times capable of absorbing about one-fourth more 

 (or 0'3 per cent.), when placed in water for a few 

 hours. This quantity is, however, rather larger than 

 could be expected of a good sample. Expressed in 

 anol^ier way, I may say that a cubic yard, or two 

 tons weight of granite, contains, in its ordinary 

 state, something more than 3^ gallons of water, and 

 some specimens can absorb nearly a gallon more on 

 being placed in pure water for a short period. It is 

 important to notice this fact, as the influence of 

 frost on stone is in proportion to the water it takes 

 up, and determines its durability. — A/iakd's Lectures 

 on Fradical Geology. 



Eestoo^-s of Dkivek-akts.— First a single ant 

 clung tightly to a branch, and then a second insect 

 crawled cautiously down its suspended body, and 

 hung to its long, outstretched limbs. Others fol- 

 lov/ed in rapid succession, until they had formed 

 a complete chain of ants, which swung about in the 

 wind. One of the largest workers then took its 

 stand immediately below the chain, held firmly to 

 the branch with its hind-limbs, and dexterously 

 caught with its forelegs the end of the living chain 

 as it swung past. The ladder was thus completed, 

 and fixed ready for the transit of insects ; and in a 

 similar way the whole tree was covered with festoons 

 of ants, until it was blackened with their sable bodies. 

 ^Homes v:itlioui liands. 



WINDOW GAEDENS AND AaUARIA. 



Eed-leaved Sea- weed {Delesseria sancjidnici) . — 

 The eight leaves of this alga, sent herewith, are 

 taken from a specimen which grew in the aquarium 

 of the Zoological Gardens, Hamburg, in the winter 

 and spring of 1865. Is any other instance known 

 of the plant having thus grown from a very young 

 state, or from seed, in a tank ? It is the first time 

 I have known it do so. I found it by accident in a 

 deep and nearly dark hole in a large tank in whicli 

 specimens were placed in the summer of ISGi, but 

 which specimens died. The present specimen is pa- 

 rasitic on the stem of some long alga (probably a 

 Freas) ; but it is also so much covered with conferva 

 that not much of it can be seen. The conferva 

 does not grow on the Delesseria leaves. Last night, 

 on clearing out the tank in question, the alga was 

 for some hours exposed to the air, and this morn- 

 ing some of the leaves were found of an orange 

 colour — the colour of death, and these leaves are 

 those now sent ; but the orange (decayed) parts are 

 not so apparent as when they were in water. But 

 there are still plenty more of much smaller leaves on 

 the same stem, and these will be watched carefully. 

 — W. Alforcl Lloyd, Keeper of the Aquarmra. 



Aquarium a^^d Eeenek^. — The salt-water aqua- 

 rium before me is about 16 inches diameter and 

 8 inches deep, covered with a bell-glass about 2 feet 

 high, but not fitting closely. The lower vessel is 

 two-thirds filled with sea-water ; in it, besides other 

 living organisms, are various anemones, of all sizes 

 and ages, gathered from difl^erent parts of our coast ; 

 fine shingle, bits of rock, coral, &c., are strewn on 

 the bottom, many of the latter are covered with 

 bright emerald green vegetation of spontaneous 

 growth. In the centre stands a tripod supporting a 

 wooden basin. The former consists of three strong 

 zinc wire legs ; both these and the basin are concealed 

 by specimens of rocks, &c., collected from various 

 places and firmly fixed with good Roman cement. 

 In the basin filled with cocoa-nut fibre we have found 

 almost any kind of common fern will grow {Adiaii- 

 tum capillus-veneris, cuneatum, pubescens, pedatum. 

 Asplenium vivipanm, gracile, and Sandersonii, v/ith 

 many others, grow well). Last year some sowed 

 themselves in the crevices of the rocks, forming a 

 pretty fringe just above the water The brushwood 

 in this miniature forest is any kind of Lycopodizm, 

 except ccesi'im, which does not succeed well with us. 

 I think succulent ferns do the best. The water is 

 in a good state, and has not been changed since last 

 October. I have grown ferns in pots in the room 

 for several years in unmixed cocoa-nut fibre witli 

 charcoal for dramage, and the "mould" never ap- 

 pcared, — Leonora. 



