266 



HARDWICKE'S SCIENCE-GOSSIP. 



similar to the one here represented, composed of 

 two slips of glass cemented on each side of a plate 

 of metal of the proper thickness, and of the form 

 shown in the figure, the light part being that which 

 is removed. If it is now filled with clean water, 

 and the middle cell placed before the microscope 

 (solar or gas) and a drop of the infusion containing 

 the animalcules put into the cell b, on the command 

 of the exhibitor the animalcules will commence 

 marching across the field of view, and to those 

 unacquainted with the -plan it will appear in obe- 

 dience to order, but which is merely their desire to 

 spread themselves. In the same manner, when the 

 cell a is full, c may be placed under the instrument, 

 and the marching again commence, the little animals 

 only being able to pass from one cell to the other 

 singly." 



Fig. 1 56. Diagram of Trough for showing Migration of 

 Infusoria. 



Mr. Pritchard claimed the merit of the introduc- 

 tion of Canada balsam as a medium for mounting 

 microscopic objects. Its value for this purpose, 

 however, was not discovered until some time after 

 the publication (in 1832) of his "Microscopic 

 Cabinet." In his " Catalogue," dated 1837, he 

 mentions objects mounted in balsam. 



The following is a list of the prices of mounted 

 objects : — 



Case of transparent objects containing 40 slides, 

 7s. 6d. 



Ditto 36 opaque objects, 7s. 6d. 



36 opaque objects mounted on cylinder, 7s. 6d. 



Objects selected from the list in sets, per dozen, 

 2s. 6d. to 18s. 



Three sections of fossil woods, cut horizontally 

 and longitudinal, showing the internal structure of 

 plants, each from 2s. 



About this time Ehrenberg commenced publish- 

 ing his observations on the Infusoria, commencing 

 with his Geographical Distribution of Infusorial 

 Animalcules in North Africa and Western Asia, 

 Berlin, 1828. In 1838 appeared his magnificent 

 work, " The Infusory Animalcules as Complete 

 Organisms," published in 2 volumes folio, contain- 

 ing 547 pages and 64 coloured plates. In 1830 

 Agardh (C. A.) published his " Conspectus criticus 

 Diatomacearum." M. De Brebesson published his 

 " Notes sur quelques Diatomees marine, rare ou peu 

 connucs du Littoral du Cherbourg," in 1S34. 



In 1S33 Kutzing published several works on the 

 Diatomacese and other Algse. From that time to 

 the present the microscope has been continually 

 improved, until it has now become an instrument of 

 precision worthy of a better employment than dis- 



playing arranged butterfly scales and Diatoms or 

 Micro-Photographs. 



In this brief history of the Microscope and 

 Microscopic Work we have endeavoured to show 

 what could be done by the very imperfect instru- 

 ments employed by Leeuwenhoek, Hooke, Swam- 

 merdam, and other early observers. 



We are apt to smile at the tests of fifty years 

 ago, with lines as close as- twenty in the thousandth 

 of an inch, requiring a magnifying power of 350 

 diameters and an angle of aperture of not less than 

 55° ! Every worker with the microscope must 

 admit that infinite credit is due to the opticians for 

 the improvements they are constantly making in 

 objectives. Eorty-four years ago an objective 

 with an angular aperture of 55° and magnifying 

 350 diameters was, perhaps, more highly-esteemed 

 than a modern glass of three times the angle of 

 aperture, and possessing an amplifying power of 

 5,000 diameters capable of showing an object not 

 more than T aoVoo or " an inch in diameter. 



It is probable that we have now nearly reached 

 the limit of magnifying power; and if the undulatory 

 theory of light be true it must necessarily follow 

 that no image can be formed of less diameter than 

 half a wave length. We must, therefore, look for 

 the more perfect correction of our lenses and im- 

 proved methods of illumination, rather than in- 

 creased magnifying power for the discovery of 

 minute structure, and we shall then probably find 

 that many of our previous opinions will have to be 

 considerably modified. Before concluding this 

 series of papers we wish to correct one or two 

 errorsl that escaped notice when revising the 

 proofs :— in page 81-, column 2, 5th line from bottom, 

 read Culpeper ; page 85, column 2, 23 lines from 

 bottom, read 1668 ; page 86, column 1, line 13 from 

 bottom, read fig. 44 ; column 2, line 2, insert fig. 

 47 after "diagram" ; page 199, column 1, line 20 

 from top, for American, read Amician. 



In conclusion I beg to thank those friends and 

 correspondents who have from time to time given 

 me valuable information. 



A BEPTILE VIVARIUM. 



PERSONS who are fond of keeping snakes and 

 other reptiles alive are sometimes rather at a 

 loss for suitable receptacles, especially if the cap- 

 ture or donation happen to occur unexpectedly. 

 This was the writer's case about a year ago, on 

 coming suddenly into possession of three Que slow- 

 worms, when the following expedient was adopted, 

 which answered so well that it is here described, as 

 it may, perhaps, be useful to others on a similar 

 occasion. Not having a vase or case unoccupied, I 

 took a box, which had formerly held some gro- 

 ceries ; its proportions were about 14 inches long, 



