148 NOTES AND MEMORANDA. 



Macldox's opinion of his " simple mount," for essentially it is the 

 same as ToUes devised, and has used for some ten years past. There 

 are some minor details of construction in which the two differ, viz. 

 Dr. M. introduces a spiral spring of two turns, Tolles a spring of 

 several turns. Maddox's spring lifts the tube, Tolies' depresses it. 

 These differences are not essential. Maddox's spring acts against one 

 steel pin screwed into the inner tube. This pin must be liable to 

 wear in its bearing in the thin inner tube ; and besides, the pressure 

 of the spring acts on one side only of the tube, having a tendency to 

 press it sideways. These defects are remedied in Tolles' mount. But 

 Dr. Maddox takes no notice of the most important point in this ar- 

 rangement, that is, moving the inside bases instead of the front base. 

 Mr. Wenham many years ago devised some means of moving the 

 middle and back bases, leaving the front base stationary. Although 

 he spoke of this plan as a gi-eat improvement on the old one, although 

 it has been highly commended by those who have had objectives spe- 

 cially mounted so since, yet it has not been adopted by the English 

 makers, or by any American except Tolles. Why ? The only ex- 

 planation seems to be, that such construction, if done well by first- 

 class workmen — and it must be done as only the best workmen can 

 do it, or it will not be satisfactory — will cost from one to three guineas 

 extra for each objective. 



Monochromatic Light in the Study of Diatoms. — Professor J. 

 Edward Smith says : — " I have recently been using monochromatic 

 light for the study of the finer diatoms. A rude ajDpliance for this 

 purpose can be arranged in a very few moments, as follows : — Take a 

 piece of thin board, say 15 x 20 inches, and provide several pieces of 

 plain cleaned glass, either light-green or blue ; spectacle glasses will 

 answer. Cut a hole of proper size through the board, and at about 

 the height of level of microscojoe stage ; this aperture to be occupied 

 by the coloured glasses, using the combination which proves to give 

 the best definition. At present I am using one pale-blue outside and 

 f<jur interior ones of light-green, all placed in contact. The com- 

 bination should be deep enough to prevent any blazing effect when 

 the full beam is turned on. Such a contrivance, so placed as to 

 transmit the solar rays to the mirror of the instrument, will prove to 

 be far superior to any lamplight illumination, and no condensers 

 required. With it, and a Tolles' -|^th dry, or yLth wet objective, I 

 have easily shown AmpMpleura pellucida on balsam in beads, under 

 high eye-piecing, and with lowest eye-piece the transverse and longitu- 

 dinal ' strife' are easily seen. Nos. 18, 19, and 20 of Moller's Probe 

 Plate, which have resisted my protracted efforts by lamplight, yield at 

 once to this illumination. Probably other combinations of coloured 

 glass may be found suj)erior to that described." 



Young Octopods at the Brighton Aquarium. — It is to be hoped 

 that the Brighton Aquarium people will some of them see the splendid 

 oj)portunities which are being daily presented of studying the de- 

 velopment of rare animals. We understand that the octopus has 

 deposited its spawn in the Aquarimn, and that it has been regularly 



