178 



THE AMEKICAN MONTHLY 



[September, 



before use, to drive off the carbon dioxide, 

 and thus destroy the zinc carbonate, the 

 trouble will be likely to disappear. I have 

 noticed that oil of cedar (used as immer- 

 sion fluid) is apt to soften or destroy the 

 zinc cement rings, if they are at all recent, 

 and mention it, because I have not seen 

 it noticed. 



T. F. C. Van Allen. 



Albany, N. Y., July 12th, 1886. 

 o 



To THE Editor : — I note a letter in the 

 Aug. number of your Journal from Mr. 

 Thompson, in reply to query from W. in 

 July number. 



He quotes ' Tuckett's Treatise.' From a 

 pretty fair acquaintance with treatises 

 on the microscope published in Enghsh, 

 from ' Hook's Micrographia,' say, 1665, 

 down, I think I can safely assert that 

 there is no such treatise as Tucketfs. 

 Could you have mistaken Mr. T's manu- 

 script, and thus read it instead of Ouekett ? 

 I have the 3d ed. of Ouekett, 1855, and it 

 is as Mr. T. states. Some years since, in 

 N. Y., in conversation with Mr. John 

 Phin, editor of the Am. Jour, of Micro- 

 scopy, in regard to older works on micro- 

 scopy, he stated that he had a copy of 

 Ouekett, 2d edition ; that it gave a plate of 

 the diatom in question, and remarks on 

 its resolution by Spencer's objectives, 

 which had been impossible till then with 

 the best glasses then made in Britain or 

 on the Continent, and that it had so galled 

 the English opticians, and raised such an 

 outcry, that (Ouekett dropped the matter 

 in his 3d edition. There should be no 

 great difficulty in finding this 2d edition 

 in some public library, or in the collection 

 of some microscopist. Practical optics is 

 a very old science dating back to the days 

 of Babylon, quite old in Europe, quite 

 young in the U. S. Through Spencer, the 

 child gave the mother the Jirst lesson on 

 increased angular aperture. His glasses, 

 in this respect, far exceeded any thing 

 then known in Europe. Further advance 

 in this direction had been proclaimed use- 

 less and impossible by the first English 

 authorities. Still, there were the facts and 

 the glasses, both stubborn things. The 

 secofidlason, and in the same direction, 

 was given by the late Mr. Tolles, a pupil 

 of Spencer, in the + 180° war which lasted 

 some years, the truth of his deductions 

 and productions being triumphantly es- 

 tablished to the satisfaction of the world, 

 and again, despite of the dictum of the 

 highest British authorities. Still, this set- 

 ting limits to the advance of science still 

 goes on, and every ten or twenty years 



we have to set them further back. Within 

 a few years a president of the Royal Micr. 

 Soc, in his annual address, fixed the 

 limits of resolution of fine lines at 100,000 

 to the inch. This did not fit existing facts 

 then, and far less since, as there is the 

 strongest possible evidence to attest that 

 it reaches to 130 or 150,000 at least. This 

 fixing of limits is an old business. In an- 

 cient times they fixed the limits of the 

 world, the ' ultima thule,' at the pillars of 

 Hercules, as the ' ne plus ultra' (nothing 

 beyond.) My namesake did not accept 

 the proposition, hence our being. Spain, 

 after this, with very pardonable vanity, 

 stamped on her coin the pillars (of Her- 

 cules) encircled with a streamer, and the 

 motto, ' plus ultra ' (further yet,) and this, 

 by the way, is the origin and ' true in- 

 wardness ' of our dollar mark, $, despite 

 several other accounts of the same. The 

 two straight lines represent the pillars 

 of Hercules, and the curved one the 

 streamer. The motto 'plus ultra,' so de- 

 cidedly American, in its origin, I think a 

 good one for our scientists while engaged 

 from time to time in setting back the vari- 

 ous ' limits ' by which they are sought to 

 be confined. In scientific matters it would 

 not seem to be safe to accept the ' dictum ' 

 of any man or body of men. The 'limit ' 

 they place is usually that which includes 

 their otvn knowledge, with very little room 

 for expansion. 



Chr. C. Brooks, Ph.D. 

 393 E. Eager St., Baltimore, Md. 



o 



A 1-25 Inch Objective. 



To THE Editor : — I received of H. R. 

 Spencer & Co. last October a ^ inch 

 objective ; it has a B.A. angle of 125°. I 

 consider this ^^ to be one of the best high 

 power objectives I have ever looked 

 through ; it resolves the most difficult 

 slides of Amphipleura in balsam with 

 plain mirror, illuminated mirror being 

 placed central and no stops in the con- 

 denser. 



All things being in good order and the 

 light in the proper direction for the work 

 in hand, it resolves the most difficult tests 

 at once. I consider this ^ of the Spen- 

 cers to be the best, or one of the best, 

 high powers that he has ever made for 

 resolution and definition, and I cannot 

 see how it can be excelled or ever equalled. 

 Its definition with glycerin and central 

 light is unrivalled. It has a good working 

 distance and works easily through a thin 

 No. I cover, and it works well with water, 

 glycerin, and homogeneous fluid, and 

 works well and gives good definition when 



