NOTES AND MEMORANDA. 85 



high summer temperatures which so often prevail in the United States, 

 it is very possible that glycerine may behave somewhat " more kindly " 

 as a preservative in that country than it will here ; though from what he 

 has been able to learn from the conversation of friends who have been 

 abroad, and from the letters of correspondents, he has been led to the 

 conclusion that the experience of the majority of histologists, both on 

 the Continent and in England, has been, in this matter, essentially the 

 same as mine. Nor does he understand Dr. Beale's language, either 

 in the article before him or in his former publications, as claiming 

 any constant or uniform permanency for glycerine preparations. Dr. 

 Beale does not tell us that all, or even the majority, or even a large 

 minority, of the thousands of preparations he has immersed in glyce- 

 rine, retained their pristine beauty and usefulness for any considerable 

 time. Is it not a fact, he would ask him, that even in his own skilful 

 hands it is only a few fortunate preparations out of many made, which 

 by some hapj>y chance survive the common ruin of the first summer ? 

 " Now, as to just what I have been able to do myself, or to have done 

 at various times by my assistants, I have not a great deal to add to my 

 former article. Dr. Beale proposes that I should get some friend in 

 whom I have ' implicit confidence,' to cross the ocean and wait on 

 him with some of the Museum specimens, for comparison with his. If 

 he really desires that any such comparison should be made, would it 

 not be much simpler for him to send me by mail, or otherwise, one or 

 two glycerine preparations of tissues which he thinks it quite im- 

 possible to display in balsam ? I would take pleasure in sending back 

 what I could, in the same way. Meanwhile, I cordially invite any 

 English or American microscopists who have seen Dr. Beale's prepa- 

 rations in his own hands, to call at the Museum in Washington, and 

 see what we have been able to do in the way of making a collection of 

 histological preparations which are likely to be permanent." 



Draw-tubes versus Deep Eye-pieces. — Mr. Stodder says in the 

 ' Lens ' for November, in reference to a paper which had previously ap- 

 peared in that journal, that the writer omitted the whole question by 

 not specifying any length of tube. " With what length of tube has 

 good definition been obtained ? Thousands are using English and 

 American instruments with tubes eight to ten inches long, giving the 

 conjugate focus ten to twelve inches from the optical centre of the 

 objective, and to that adding some inches of draw-tube. Now, all 

 these will undoubtedly agree that the ' perfection, clearness, and 

 brightness ' of the image depend upon the skill of the maker in cor- 

 recting ' the spherical and chromatic aberration,' and not on the 

 length of tube or power of eye-piece entirely. He has by him photo- 

 graphs of Amphipleura pellucida, taken by Col. Dr. Woodward, of 

 Washington, with a Tolles' objective (a little less than one-fifth inch 

 focus) at 48 inches distance from the objective : this is equal to a 

 pretty long tube. Now, this photograph bears enlarging twenty dia- 

 meters, and still shows ' clear and bright.' But he has other photo- 

 graphs by Dr. Woodward of the same object, taken with Powell and 

 Lealand's T Vth (so-called) and with Tolles' T \th at 7 feet 6 inches 

 distance, still giving good definition, and bearing a low-power eye- 



