HARDWICKE'S SCIENCE- G SSIP. 



255 



purpose ; and if carefully applied, so as to fill up 

 the angular furrow at the margin of the cover, it 

 will make a very neat finish." I never myself adopt 

 the plan of letting the damar run under by capillary 

 attraction, always preferring to drop the damar on 

 the object, and then lay the cover on that. There 

 is no great necessity for warming either slide or 

 cover before mounting. In my cabinet I have many 

 objects which I have mounted both ways, and the 

 results are quite the same ; indeed, of the two I 

 prefer not to warm the slide. I have both heard 

 and read complaints of this medium by those who 

 have had it made up from a receipt, and as two of 

 the chief outcries are likely to affect both the damar 

 in tube and the damar out, I will speak of them. 



Firstly, many complain of the number of air- 

 bubbles that rise while mounting. Now, I think 

 that with a very little care this may be easily 

 obviated, /never find any trouble from this cause, 

 and I go to work in the following manner : Let me 

 say that I am about to mount the leg and foot of a 

 wasp ; of course it has been treated before in the 

 same manner as if it were to be mounted in balsam. 

 I take a well-cleaned glass slip, and putting a 

 centerer under it, remove the object from the spirits 

 of turpentine, and lay it by means of forceps on the 

 slide ; next see that the claws are well separated, 

 and then gently squeeze the tube of damar, and 

 when I see sufficient damar to cover the object, lay 

 the thin cover thereon, and gently press. Possibly 

 my object is not quite flat, and up goes the cover 

 on one side, while air-bubbles rush in at the other. 

 The moment I see this I take a spring mounting 

 clip, and clip the object, then put away in a 

 moderately warm place. In two or three days, on 

 removing the clip, I find the object as free from air- 

 bubbles as it can be. Thin fine objects need have 

 no clip, as the air-bubbles will depart directly the 

 cover is laid on. Looking over my back volumes 

 of Science-Gossip, I find, in the volume for 1873, 

 page 110, that a correspondent, signing himself 

 " W. S. Palmer," complains of the little use he 

 finds damar, .owing to these air-bubbles ; and he 

 further asks whether any of the readers of Science- 

 Gossip have been more successful ? As far as I can 

 see, no one has given his experience, but he will 

 be able to see from this that at least one corre- 

 spondent has been successful ; and should W. S. 

 Palmer still And so great a difficulty in mounting 

 with this medium, if he will send me his address, I 

 shall be most happy to send him a slide mounted in 

 the way I have described. 



Then, secondly, many say they can do nothing 

 with damar, because it is so liquid that it will not 

 dry. Now, I admit that there is more to be said 

 against damar for this than from the complaint of 

 air-bubbles ; but still I do not think many of my 

 objects have been spoilt through this. Certainly, I 

 find that even in a warm place the slide takes more 



than too days to set; for instance, some slides that 

 I mounted on March 14th were not ready to finish 

 off until March 21st ; but then the result was good, 

 and I do not think any microscopist would object 

 to waiting a little, providing the result in the end 



was gained. 



Lastly, as to finishing off, some varnish must, of 

 course, be used, and I always use the asphalte var- 

 nish, which I buy at the optician's— a bottie costs 

 sixpence. I always have used this, and continue to 

 do so (though it is useless when mounting with 

 glycerine jelly), because I find it is in every way 

 good. Run a good ring round, and I think there is 

 no need for fear about the cover moving; if, how- 

 ever, you like a pretty finish, run round a ring of 

 red sealing-wax varnish, and then just at the 

 edge of that a ring of asphalte varnish, and the 

 effect will be very good. I think I can do nothing 

 further now than advise every reader of this to give 

 the damar in tube a fair trial ; it can be obtained 

 from the preparer, Walter White, Litcham, Norfolk, 

 or through any optician, which perhaps is the best 

 mode of procuring it, as then it gets to be known 

 more generally, for I find that as a rule it is not 

 kept in stock. I never was so successful with 

 balsam as I am with damar, and I trust all my 

 readers may shortly say the same. 



Eedland. Chakles Williams. 



MICROSCOPY. 



Vitality of Eggs. — M. Colosanti has recently 

 made some very interesting experiments on the 

 duration of vitality of the macula germinativa. 

 Experimenting with hens' eggs, he found that in the 

 first twenty days after the egg is deposited, develop- 

 ment of a chicken may take place; after that 

 epoch development is not the rule, but the exception. 

 But the germinal spots which did not produce 

 chickens always showed some development, though 

 incomplete. This shows that the evolution is not 

 the result of a force which exists or does not exist 

 in a germ, but rather of a force subjected to quan- 

 titative modification, and which expires gradually. 



Professor Ehrenberg. —This famous natu- 

 ralist, with whose researches every microscopist 

 must have come into contact at some period of his 

 life, died at the end of June last at a very advanced 

 age. Although a great many of his views have 

 been modified during his life, his work has only 

 proved that it is easier to revise than to discover. 

 Ehrenberg was a great man, and all true naturalists 

 will do homage to his intellectual worth. 



Wythe's Illuminator. — In the American Natu- 

 ralist for July, Dr. J. H. Wythe recommends for 

 oblique illumination a right-angled prism, with a 

 plano-convex lens, cemented to and covering one of 



