206 MEMORANDA. 



bottle at the time. It will be observed that the string is 

 passed through a small ring at the top of the socket : this 

 answers the double purpose of preventing the loss of the cork 

 by its becoming detached from the bottle, and also of saving 

 the bottle itself, should it by any chance become loosened 

 from the stick while in the water ; for in this case, as will be 

 seen, it will still be held by the string and the cork to which 

 it is fastened. I find, however, that practically there is no 

 probability of this happening, as the gutta percha socket 

 holds the end of the stick with a considerable degree of 

 firmness, requiring some little force to detach it. The bottle 

 can, of course, be used at any time without the cork, by 

 simply drawing the string sufficiently tight to keep it out of 

 the way. I have used gutta percha in the construction of 

 the various parts, on account of the extreme facility with 

 which it can be moulded into the required shape, and as any 

 one can with it fit up a bottle in a short time, and at the cost 

 of a few pence. But, doubtless, several other materials will 

 suggest themselves, as convenience might place Avithin reach; 

 the socket, b, for instance, might be made of metal, with a 

 screw corresponding to one at the end of the stick or rod, so 

 as to allow of the substitution of a small net or a knife, for 

 cutting off pieces of aquatic plants, &c. It might be found 

 convenient by some to have the cork permanently fixed to 

 the mouth of the bottle by means of a slight spring (which 

 may be applied in various ways) ; it would thus be always 

 ready for use, and the pulling of the string would only lift up 

 or draw aside the cork, which, returning immediately to 

 its place on slackening the string, might keep in some of the 

 larger insects that would perhaps otherwise escape. — James 

 Smith. 



On an Erecting Prism. — The instrument represented in the 

 annexed cut is intended to 

 supply the place of the first 

 erecting prism constructed 

 by us, the use of which is 

 attended with some incon- 

 veniences. Being placed 

 above the upper lens, it 

 obliges the eye to be held 

 at some distance from the 

 locus of the ocular; sp that, 

 in order to obtain a view of 

 the entire field, it is neces- 

 sary to alter one's position. 



In the new instrument, the prism is placed between the 



