HARDWICKE'S SCIENGE-GOSS IP. 



203 



on the means, but continually searching out and 

 examiniiig " whatsoever things are true." 



Edward* C. Lefroy. 



f HOW TO EIX DEVICES OE DIATOMS. 



OOME of your correspondents have made in- 

 '^ quiries how to/.r devices of diatoms. There 

 is some secret, about doing it which the best diato- 

 mists hold very fast. After many hundreds of 

 failures, I have " wriggled " my way to the outskirts 

 (only the outskirts) of the secret ; and what I know 

 I shall be glad to tell. We must presume that the 

 diatoms are perfectly clean, that a "dip" of the 

 material containing them has been evaporated on a 

 slip, and that the hair from a cow's neck (which is 

 the best tool) has been duly mounted in a wooden 

 handle. When a diatom is picked up by the hair 

 from the dip, under a I^-inch power (and after 

 practice they may be 'picked up at eight or ten 

 per minute), the question is where to put it. Some 

 say, "into a minute drop of water." This is 

 easiest, but no one can arrange diatoms in such a 

 drop. I put them on a prepared (glazed) cover. 

 I take distilled water and filtered gum (either 

 arable or tragacanth, but I prefer the latter), both 

 being chemically and microscopically clean (if I 

 can get them clean : I never have as yet), and info 

 a 2-ounce phial put, say one ounce of the water 

 and five or six''drops of the gum. I then clean 

 covers (I glaze 50 or 100 at a sitting), and place 

 them on a rack of wood, i.e. six pieces, 6 inches 

 long, I inch broad, and \ iuch thick, formed into a 

 " rack" by having pieces of copper wire run through 

 the lot near to each end, so that the bars of the rack, 

 slid on the wires, may be altered to suit different 

 sizes of covers. I then take a dip of the gum-water 

 in a very-fine mouthed pipette (never putting the 

 pipette more than halfway into the water, and 

 throwing away the first four dips for fear of dirt), 

 and, having the rack full of covers, allow a minute 

 drop to escape on the centre of each cover, holding 

 the cover with a clean needle to prevent its being 

 lifted when I withdraw the pipette. I tlien transfer 

 the loaded rack to the hot plate. Here the useful- 

 ness of the rack will be felt, as it reduces to a 

 minimum the exposure of the covers to the vile 

 inappreciable dust. And, by the way, to glaze 

 covers or mount diatoms on any but the calmest of 

 days is absolutely impossible. The glazed covers, 

 when dry, I store under a well closed glass shade. 

 One of these covers I place on a wooden slide 

 (they slip on glass) perforated with a |-ineh hole 

 (or three such slides may be used at once, or one 

 slide with three holes, so as to select three species 

 from the same dip), and have it at a handy distance 

 (three or four inches) from the stage. On this 

 cover I put the diatoms, picked out with the cow's 



hair aforesaid. If the diatoms be plentiful, I simply 

 "dab" the hair gently three or four times on the 

 cover to disengage the frustule : by this mode half 

 the diatoms are lost and half the time is saved. 

 But if the valve be a gem {A. Kitfonil to wit), I 

 hold it within the field of the microscope with my 

 right hand (hand-rests are supposed) whilst, with 

 my left, I remove the dip and replace it with the 

 wooden slide, disengaging the valve very carefully 

 in the centre of the glazed dot. When sufficient 

 frustules have been placed on a cover to form a 

 device (cross, star, initials, &c.), I place, push, 

 coax, or drive them, with the hair, under a li-inch 

 objective, into the required form. In this ope- 

 ration, delicacy of touch, coolness, and patience are 

 somewhat helpful; moreover, to steady the ope- 

 rating hand with the other is an advantage. This 

 done, the cover with its device must be brought 

 close to (just within) the mouth, and breathed on — 

 one long slow breath. Diatoms will not bear 

 coughing at. But if all this has been done success- 

 fully, diffi':?ulty is at an end. The cover must be 

 dried on the hot plate and then turned over on to a 

 drop of balsam and benzole, or damar, in the centre 

 of a slide ; and, if the glaze be the proper thickness 

 the balsam may be boiled to one's heart's con- 

 tent without moving a single valve, and the slide 

 finished there and then. As I said at the outset, 

 there is a secret beyond all this (I wish some one 

 would piiblish it), but I have proved that by this 

 process the fixing of any number of diatoms in any 

 device is only a question of time, patience, and 

 manipulatory skill. In closing, let me say three 

 things to those who aspire to be " diatomaniacs ": — • 



1. Never hope for one drop of clean water, unless 

 you distil it yourself, and don't be sanguine then ; 



2. Place your diatoms "on their backs" in the gum, 

 else they will retain air, which nothing can expel j 



3. " Mind your eye," or rather your eyes, for mine 

 have been so strained with arranging diatoms that 

 I have not dared to work with the instrument for 

 several months. J. K. Jackson. 



NOTES ON THE LEPIDOPTERA OF 

 GUERNSEY. 



IN vol. viii. p. 65, of Science- Gossip, Mr, 

 W, H. Booth has given us the result of his 

 observations on the butterflies of the Channel Is- 

 lands ; but his experience appears to have been 

 mostly conSued to Jersey ; and as any reliable in- 

 formation which can be collected respecting the 

 entomology of different parts of the kingdom must 

 greatly assist us in forming an accurate idea of the 

 distribution of species, I will, with your permission, 

 add a few notes on the lepidoptera of Guernsey 

 from observations which I have made during a resi- 

 dence of several years in that island. 



