1881.J 



MICROSCOPICAL JOURNAL. 



75 



be aliquot parts, either of the British 

 Imperial Yard "' Bronze i," or of the 

 " Metre des Archives." 



At present he will make the follow- 

 ing patterns : 



1. loi lines .001 inch, and loi lines 

 .001 *""• with the first line in each 

 common to both, price $2.00. 



2. 301 lines, 100 coarse, 100 very 

 fine, for high powers, loi coarse, all 



.oi"""- price $2.50. 



3. 501 lines .01 '"", and 501 lines 

 -gVoo-irich, price $5.00. 



4. looi lines .01 ™™- and looi lines 

 g-5*o 0-inch, price $10.00 



5. Same as the preceeding one but 

 with both sets of lines double, that is, 

 ruled both with fine and with coarse 

 lines, price $15.00. In all the above, 

 the 5th and loth lines, are longer 

 than the others. 



We believe that these are the only- 

 micrometers that are perfectly reliable, 

 and it is to be hoped that microscopists 

 will show their appreciation of the 

 work of Prof. Rogers, the value of 

 ^ which is far above any estimate of a 

 m commercial nature, by possessing 

 themselves of one of his excellent 

 plates. 



The object in ruling the lines g^-gV^ 

 of an inch apart is to permit of ready 

 comparison with the .01""" lines, these 

 spaces being approximately equal. 

 It will be seen that one band acts as 

 a vernier to the other. 



Preservative for Alg^. — M. 

 Paul Petit has experimented in or- 

 der to obtain a preservative liquid 

 for algae, and has finally prepared 

 one which seems to be quite satisfac- 

 tory for the purpose. 



It is composed as follows : Cam- 

 phorated water and distilled water, of 

 each 50 grammes, glacial acetic acid, 

 .5 gr., crystallized chloride of copper 

 and crystallized nitrate of copper, of 

 each .2 grammes ; dissolve and filter. 



Preparations made with this liquid 

 have retained their living appearance 

 and green color after exposure to 

 the direct light of day for a year. 

 Spirogyra, Uloihrtx, and especially 



Desmids {Penium Ncegeli and Mi- 

 crasterias crenulata), have long re- 

 tained their freshness in the solution. 

 It will be observed that the salts of 

 copper have been made use of to pre- 

 serve the color, just as they are, on 

 a larger scale, in preparing legumes 

 for the market. 



We have long felt the need of a 

 solution of this kind,' and sincerely, 

 hope that M. Petit's solution will 

 meet our wants. Our own experi- 

 ments have not been productive of 

 good results. However, the loss of 

 color in our specimens has been a 

 matter of secondary importance. The 

 great difficulty with us has been to 

 preserve the natural arrangement of 

 the cell-contents, and after trying 

 many of the solutions that have been 

 recommended we have fallen back 

 upon pure water, or water mixed, with 

 about one-tenth of its volume, of 

 strong lime-water. We propose to 

 try M. Petit's solution immediately. 

 o 



Movement of Diatoms. — The 

 contribution from Mr. Cox, which is 

 printed this month, will doubtless 

 lead many readers to give special 

 attention to this curious phenomenon. 

 It should be understood that the 

 cause of the motion is now as myster- 

 ious as ever — no satisfactory explana- 

 tion of it has yet been given. The 

 presumption that it is the result of 

 osmose is scarcely tenable, from a 

 physical point of view. The pheno- 

 mena of osmose depend upon differ- 

 ences in the density of two miscible 

 fluids which are separated by a mem- 

 brane, and they are apparently some- 

 what related to capillary phenomena. 

 With very few exceptions, the pre- 

 vailing flow is from the rarer to the 

 denser medium, so that this action, 

 if it took place in the diatoms, would 

 tend in the wrong direction to pro- 

 duce motion of the frustules. More- 

 over, it is difficult to conceive of any 

 physiological cause for the reversal 

 of the current after it is once estab- 

 lished in the natural direction. It 

 can hardly be maintained that osmose 



