38 



SCIENCE-GOSSIP. 



rF£B. 1, 1865. 



qumng the art of the optician to reveal their 

 beautiful diversity of forms, and their extreme 

 delicacy of structure. Tliey are inhabitants 

 of the water, and so widely distributed, that 

 there is scarcely a pool, a ditch, or a v/ater- 

 course where they are not to be found, at- 

 tached to svibmerged weeds, or mixed with 

 floating debris, or deposited on old piles sub- 

 ject to tidal iufluences, or forming a cover- 

 ing on the surface of the mud, arranged in 

 patches, and varying in colour from a yellow- 

 ish brown to a dark chocolate. Some species 

 are indigenous to fresli, some to salt, and 

 some to brackish water, but those common to 

 the one are never fouiid in a lively and 

 healthy state in the other. 



In the early history of Diatomacsw, they 

 were placed by naturalists in the animal 

 kingdom, in consequence of their curious move- 

 ments ; a more intimate acquaintance with 

 their nature and habits, acquired by the aid 

 of improved microscopes, and confirmed by 

 chemical experiments, has resulted in their 

 being transferred to the vegetable kingdom 

 by the unanimous consent of all competent 

 judges. It is now ascertained that the power 

 of locomotion is not peculiar to the Diato- 

 rjiacece, but that many of the simple plants, 

 such as Oscillatoria, the Desmidiacece, Fro- 

 tococcus, and others, possess this power in com- 

 mon with the Diatoms, and some of them, in 

 certain stages of their existence, are much 

 more active in tlieir movements than any of 

 the Diatomacece. 



The chai'acteristic feature of the Diatom is 

 its silicious envelope covered with a net-work 

 of fine markings, diversified in pattern, and 

 in some of the species so exquisitely delicate 

 as to require the best objectives and the high- 

 est powers to resolve them. Eeliig composed 

 of silica, these frustules are indestructible by 

 the usual agents of decomposition ; when, 

 therefore, they are cleansed by being boiled 

 for a few minutes in hydrochloric or nitric 

 acid, they become objects of j^ermanent in- 

 tei'est, and may be preserved by mounting, 

 either dry or in Canada balsam. 



In order to secure clean and good specimens 

 for mounting, it is absolutely necessary to 

 separate the Diatoms from all foreign matter, 

 which unavoidably becomes mixed with them 

 in collecting. The following is a plan I have 

 tried with great success. On returning home 

 allow your bottles to stand for an hour, by 

 which time the Diatoms and debris will have 

 settled at the bottom, pour ofi" the greater 

 portion of the water, then shaking the bottle 

 briskly, empty its contents into a soup-plate, 

 place the plate in a window for an hour or 



two, when it will be found that the Diatoms, 

 attracted by the light, will have arranged 

 themselves on the surface of the mud ; by 

 gently rotating the plate they become loosened 

 and may be poured ofii" in a pure state, and are 

 ready for being examined alive, or for boiling 

 in acid. 



In collecting Diatoms, half a dozen wide- 

 mouthed bottles, a large-bowled spoon as thin 

 as possible, and a stick with a hook at one 

 end, are all the apparatus required. The 

 spoon for carefully skimming the mud, the 

 stick for pulling in any submerged plants or 

 floating rubbish, and the bottles to hold your 

 gatherings, taking care to place the different 

 kinds in separate bottles, being furnished with 

 a Coddington lens to examine your specimens 

 on the spot. 



The marine forms of Diatomacece may fre- 

 quently be found attached to seaweed ; but 

 some of the rarer kinds must be sought for 

 from the stomach of lobsters, oysters, whelks, 

 and other mollusks. 



The favourite habitats of those common to 

 brackish water are marsh-ditches exposed to 

 tidal influences, where they may generally be 

 obtained in great quantities and many varie- 

 ties. 



The best localities near London are the 

 marshes at Erith on the opposite side of the 

 road from the entrance to the Railway station, 

 and Swanscombe Salt Marsh, lying towards 

 the river, about half a mile from Northfleet 

 Railway Station. At both of these places 

 I have always been able to get many inter- 

 esting forms, together v/ith fine specimens ot 

 living Gromia, and a variety of beautiful 

 animal Infiisoria. Others may be procured 

 from the marsh ditches at North Woolwich, 

 immediately beyond the Gardens by the 

 Railway Station. 



Fresh water Diatoms, in one form or other, 

 are almost ubiquitous. They may be found 

 deposited in brown tufts on the sides and 

 bottom of nearly every clean ditch and every 

 running stream. They line the sides oi the 

 locks up the river, fringe the leaves of the 

 larger water i.nits, and float in every collec- 

 tion of scu.. . Pinnularia cusjndata, Stau- 

 roneis, &c., may be obtained from a rill run- 

 ning across Kestou Common, near Bromley, 

 Kent, and all these forms, together with the 

 beautiful Surirella hiseriata and Surirella 

 splendida, abound in the boggy pools on 

 Winter Down, lying to the right of the main 

 road one and a-half or two m.iles through 

 Esher, oj^posite to Claremont Park. 



I must reserve a few remarks upon the 

 subject of illumination, and the best mode of 



