46 



KNOWLEDGE, 



[Febrcaby, 1903. 



the highest powers can be used, and no deterioration in defini- 

 tion will result. Those who may not think it necessary to go 

 so far as is here sngarested. may with advantage fit a tourmaline 

 over the eyepiece only to act as the analyser, and this will polarise 

 perfectly well in conjunction with a prism in the substage. 



Tourmalines have not been generally employed on account 

 of the difhculty of securing suitable pieces and the high cost of 

 such ; but if a general demand were to arise there is no doubt 

 that with an effort it could be met. It should be emphasised 

 that the plate used over the eyepiece if at all thick or dark will 

 materially diminish the brightness of the image. Poor tour- 

 mahnes will polarise, but without that brilliance which adds to 

 the beanty of the effects. 



Mr. Nelson particularly points out that an apochromatic 

 condenser should not be used in polariscopic work, because the 

 fluorite, which is used in its construction, will also be polarised. 



NOTES AND QUERIES. 



J. nnh.—Ur. Mason, of 69, Park Road, Clapham, S.W., 

 supplies specimens ready prepared for mounting. If you 

 applied to him for a list you would no doubt be able to obtain 

 what you required. 



P. B. Gray. — It is almost impossible to identify the specimen 

 you describe and sketch without actually seeing it, but it 

 probably is Anohium paniceum. This is a common pest in 

 stores, &c. 



General Warrand. — The specimen you describe and sketch 

 is no doubt the test of the Rhizopod Arrellii ruJi/uris or 

 A . dhcoides. The best cement to attach ordinary glass cells to 

 slides is either gold size, HoUis's glue, or Miller's cement. The 

 ]>ermanence of the preparations depends on the finishing varnish 

 which you use. Mr. Rousselet has given many years of experi- 

 ment to this particular subject, and he now recommends that 

 the clo-sing of the cell should be first with a coat of a varnish 

 consisting of two-thiius damar in benzole and one-third gold 

 size, then two coats of pure shellac dissolved in alcohol, and 

 finally four to six coats of pure gold size. Each layer of 

 cement must be allowed to dry thoroughly well ; three days for 

 each layer is not too long. 



W. D. Dade. — The specimens of which you send a sketch for 

 identification are probably Heiniophryu, henedeti/ Fruip. It 

 appears to be a salt-water Infusorian. 



ir. P. — The most complete work for naming Diatoms is 

 Schmidt's Atlas. This has been published in separate parts, 

 which now number sixty. The value of this work is between 

 £l;i and HiO, according to its state of preservation. A less 

 expensive book is Van Heurck's " The Study of Diatomaceae," 

 translated by Mi'. Wynne E. Baxter. The price of this is .'lOs. 



J. E. Storei/. — It is almost impossible to indicate in print 

 tests for objectives of larger aperture such as you possess, 

 because some workers are able to do so much more with their 

 lenses than others, and it would probably happen that you 

 would still be in possession of good objectives even if you 

 could not accomplish the same work as others. Experienced 

 workers can usually form a verj- accurate opinion of a lens 

 with simple rather than extreme tests, but it would be 

 impossible to give reasons for deductions in a reply such as 

 this. Perhaps some reader may know the refractive indices of 

 Farrant's medium, glycerine jelly, and acetate of copper 

 solution. 



Rev. S. R. Craig. — Notes from time to time appear on photo- 

 micrography, and an attempt is being made at present to give 

 hints on aspects of the subject which are not nsnally treated. 

 I may be glad of the loan of your photographs at a subsequent 

 date. 



W. H. — To mount vinegar eels {AnguiUula aceti) add a little 

 chloroform to the vinegar to kill the eels. When the eels have 

 settled to the bottom of the bottle, pour off the vinegar, and 

 add camphor water or carbolized water. Mount in a shallow 

 cell in the same fluid. 



Consultants. — I shall be very glad of the assistance of a 

 reader in the naming of polyzoa, algae, etc. 



Communications and enquiries on Microscopical matters are 

 cordially invited, and should he addressed to M. I. CROSS, 

 Knowledge Office, 326, High Holborn, W.C. 



NOTES ON COMETS AND METEORS. 



By W. F. Denning, f.r.a.s. 

 PBREiNg's Comet (1902 b). — This comet will be visible in the 

 evening sky before luoonrise on February !•'! and ensuing nights. 

 Towards the end of the first week in Mnreh moonlight will obliterate 

 the object, and it will Imrdly be seen again in ordinary telescopes 

 owing to its rapid decline in apparent brightness. At about the 

 middle of February the comet souths soon after 9 p.m.. but will be 

 only some 15 degrees above the horizon at Greenwich. Moving rather 

 quickly to the north-west it will south at about 8 p.m. on February 

 27, at an altitude at about 25 degrees. Its approximate path amongst 

 the star^ of Canis Major is shown on the following diagram. A little 

 sweeping in the position indicated will probably reveal the comet as 

 an eloilgated nebidous object of about the same apparent brightness 

 a« when first discovered on the morning of September 1 last. 



Path of Perrine's Comet (1902 B). 1903, February 11, to March 7. 

 GiACOBiNi's Comet (1902 n). — This comet will be somewhat 

 brighter than in preceding months, though still very inconspicuous. 

 Its favourable position in the heavens will enable it to be well 

 observed during the last half of February. On December 30, as 

 viewed in a 10 inch reflector by the writer at Bristol, the comet 

 appeared about magnitude 1 1 and 30" in diameter. The following is 

 an epheraeris : — 



E.A. 



Date 



1903. 



January 26 



February 11 



27 



March 15 



Dec. 



April 

 May 



16 



The Gkeat Meteorite of Siir.\LOA, Mexico. — An interesting 

 description of a visit to, and analysis of, this object is given by Mr. 

 H. A. Ward, of Rochester, New York, in the American Geologist for 

 October last. The great meteorite lies on a farm about seven miles 

 due south of Baeubirito. an old mining town on the Eio Sinaloa, in 

 latitude 26°, longitude 107° W. The meteorite is described as " a, 

 long monstrous boulder of black iron, which seemed to be still burrow- 

 ing to hide itself from the upper world." By the aid of 28 men the 

 object was uncovered and found to be 13 ft. ! in. long, 6 ft. 2in wide 

 and 5 ft. 4 in. ihicli. Mr. Ward concluded that this body is the 

 largest and heaviest of its kind known to exist on our globe, and 

 estimates its weight as 50 tons. A piece weighing 11 pounds was 

 detached, and on being polished and etched the Widmanstatten 

 figures were exliibited in a beautiful manner. Prof. J. E. Whitfield, 

 of Philadelphia, gives an analysis as follows : — 



Jjpecific Gravity 7'69 



Iron ... 88-944 I Sulphur ... 0005 

 Nickel ... 6-979 Phosphorus ... 0154 

 Cobalt ... 0-211 Silica trace. 



