Jan. 1, 1867.] 



HARDWICKE'S SCIENCE-GOSSIP. 



all the air before it. The slides may now be put on 

 one side in a flat position for a day or so before they 

 are subjected to heat ; then place them on a tray, 

 still in a flat position, and put them in the oven, 

 after the fire has been taken out ; when, with two or 

 three nights' baking, the balsam will become quite 

 hard and the slides can be cleaned. For this opera- 

 tion I should recommend an old penknife blade with 

 a sharp point heated in the flame of the spirit lamp, 

 and run round the cover ; the balsam can then be 

 chipped off without the risk of chipping the cover. 



The above method answers very well if you can 

 depend upon the objects being thoroughly clean be- 

 fore the cover is tied on, but with some this is un- 

 certain, as they require well pressing before the 

 fatty matter they contain can be got rid of. As a 

 more satisfactory plan I prefer the following. 



After my objects have soaked a sufficient time in 

 the liquor potasses, I place them between two slides; 

 by adopting this plan I can dry a dozen or more 

 small objects at one time. I then press them with 

 one of the common wood clips, and when dry I 

 remove tnem from the slide and immerse them in 

 turpentine. When they are ready for mounting, I 

 " centre " them on the slides, and for this purpose I 

 use a card-board template cut to the size of the slide 

 (three inches by one inch), coloured black on one 

 side, with the exception of a white disc in the centre, 

 which I leave about five-eighths of an inch in 

 diameter. On the other side I colour the disc black 

 and leave the ground white ; the black one I use for 

 diatoms, &c, and the white one for entomological 

 subjects, but the adaptability of each will be readily 

 ascertained when once made. I place the slide on the 

 template and arrange the object in the centre, then 

 drop on the cover, the template being a guide for 

 this also. I have by my side a number of pieces of 

 strong thread, about six inches long, already looped 

 up ready for tying on the cover. When the latter is 

 in its place, I drop the template and slip on one of 

 these loops, place one end between my teeth and the 

 other in my right hand and tighten. The knot may 

 then be secured and the slide put on one side, on 

 edge, to drain off the turpentine ; in this manner two 

 dozen slides or more can be put up in an hour, and 

 by that time the first one put up is ready for the 

 balsam, which can be applied as previously de- 

 scribed. 



I stated in a former part of this paper, that in 

 mounting diatoms I preferred the ordinary balsam, 

 and for this reason, viz., the diatoms can, without 

 injury, be subjected to a much greater heat than 

 animal objects, and consequently the balsam, by 

 being so heated, will harden more rapidly than even 

 if mounted with the chloroform. Eor this purpose 

 the older the balsam is the better. After evaporat- 

 ing the fluid containing the diatoms on the slide, I 

 drop on a small globule of the balsam and place the 

 cover on its summit and hold the slide over the 



lamp. As the balsam warms, the cover will gradually 

 descend to its place without the least chance of air 

 bubbles being confined ; a little gentle pressure and 

 the cover will be secure. 



Clapham. James Rowley. 



DIATOMS. 



MANY persons have heard of these beautiful 

 objects, and those who possess a microscope 

 have no doubt often wished to have specimens to 

 examine ; and the object of this paper is to tell them 

 when, where, and how to collect and mount them in 

 the most advantageous manner. 



The Diatomacere (for that is the name of the'group 

 I intend to describe) may be collected always, as 

 some one of the many varieties may be foimd in 

 almost any pond or brook ; but the most beautiful 

 are found in the mouths of tidal rivers, or in fossil 

 deposits. 



A diatom is characterized by having a flinty case 

 or shell, beautifully marked with lines, or rows of 

 dots ; but these are often so fine and close together 

 that they cannot be distinguished, except with a 

 well-constructed instrument and high powers (a 

 i-inch objective will do for most), and this has led 

 to the employment of some of these as test-objects 

 — that is to say, that if one glass will define the 

 markings better than another it is considered more 

 fit for scientific purposes; and so great is the dif- 

 ference between the size and distance apart of the 

 markings, that some may be used as tests for the 

 low powers, while others can only be used for the 

 highest. 



Many of these beautiful forms can be found living 

 in the Thames, and other rivers on our own coasts. 

 In the months of April, May, September, October, 

 and November they will be found in the greatest 

 abundance and variety; the salt marshes on the 

 banks of most of the rivers will also well repay the 

 trouble of searching for them. 



Supposing the reader to be in London, and wishes 

 to collect these interesting objects for himself, I 

 should advise him to go to Southend (which may be 

 reached by the Tilbury and Southend line, starting 

 from Fenchurch Street station), which is as good a 

 place as any other for the purpose of collecting the 

 objects under discussion"; the mode of doing which 

 is to gather the seaweeds at low tide, taking care to 

 take as little sand with them as possible, and at 

 once put them into a bottle of sea-water, if it is 

 desired to examine the living forms in their natural 

 position on the weed. But if their flinty cases are 

 wanted to exhibit the markings, the weeds may be 

 put, dry, into a bag; and, on reaching home, they are 

 to be plunged into a jar of fresh water for half an 

 hour, which will kill the animalculse attached ; and 

 when the weeds are rubbed and stirred about in the 

 water, they come off and form a cloud of muddiness, 



