22 



KNOWLEDGE. 



[January 1, 1900. 



In the course of some petrological investigations on the north 

 shore of Lake Superior, Mr. A. P. Coleman discovered a new 

 mineral, at Heron Bay, Lake Superior, which he has named 

 Heronitr, and which he describes at length in the Journal of 

 Geolof/;/. It is a dike rock, consisting essentially of analcite, 

 orthoolase, plagioclase, and cegyrite, the analcite having the 

 character of a base in which the other minerals form r.adiating 

 groups of crystals. The analcite clearly represents the magma 

 left after the crystallization of the embedded minerals, and it 

 is evident that it can be formed only from a magma highly 

 charged with water, and therefore under pressure. 



The labelling of microscopic objects, when done properly, 

 forms a no unimportant part of the training of a microscopist. 

 Apart from the discipline that it affords in habits of painstaking 

 research, the systematic record that a label contains is a great 

 time saver to the student, inasmuch as, when it is necessary to 

 refer to the object again or to comp.are it with a series of objects 

 belonging to the same genus, he is enabled to see at a glance 

 the relation that each object bears to the others in the system 

 of classification that is adopted, thus rendering further references 

 to text and note books unnecessary. For these reasons the 

 following example has much to recommend it. The labels 



should be printed in sheets and details filled in before the labels 

 are trimmed to size. They are placed on the slide, one on 

 either side of the object. 



Minute soft-bodied insects do not lend themselves to methods 

 of preparation that will enable them to be kept in a condition 

 serviceable for subsequent scientific study. Alcohol deprives 

 them of their colour, and balsam frequently distorts, and so 

 destroys the characteristics of venation and of jointed 

 appendages. The method of roasting by the sudden application 

 of intense heat has hitherto proved itself to be one of the best 

 means of dry preservation. For Aphides the following 

 procedure gives satisfactory results. The living Aphis is put on 

 a sheet of white paper, and at the moment when it is in the 

 desii-ed position the pa|)er is held over a flame, and in an instant 

 it will be dead and will ret.ain the attitude. Then put it, still 

 on the paper, into an oven ; or, still better, hold it over the 

 heated tin, carefully watching the drying and moving the paper 

 about in order to prevent it getting singed. The roasting is 

 quickly accomplished in either way. If the paper burns brown 

 it is a sign that caution is requisite. To pierce these brittle 

 preparations is hazardous, and it is a better way to mount them 

 with gum in a dry cell. 



The question of the limit of resolving power of objectives 

 is discussed by Dr. L. B. Twitchell, who points out that up to 

 the present, ICobert's twentieth band, 225,190 lines to an inch, 

 has never been resolved, and, theoretically, with white light 

 only 146,543 lines per inch can be distinguished. By utilizing, 

 however, the shorter actinic rays and a photographic plate, 

 theoretically 193,037 lines per inch should be resolved — that is, 

 effects beyond the jiossibility of ocular vision. 



Mr. G. E. Stone descants, in the current issue of the Journal 

 of Applied Mi(^rogco2}y, on the advantages of formalin as a 

 preservative for botanical specimens. He has used formalin in 

 his laboratory for six years for the display of the morphological, 

 physiological, pathological and ecological characteristics of plants 

 with most satisfactory results. The strength of the formalin 

 solution used for preserving specimens is four parts of the forty 

 i)er cent, solution to one hundred parts of water. Two to three 

 parts to one hundred have been tried, but solutions of this 

 strength have not (jroved satisfactory. Most of the specimens 

 have been kept in a 4-100 parts solution for five years without 

 renewing, and with the exception of a slight tendency to form 

 a precipitate in some of the jars, they are as clear as ever. 

 Formalin solution gives clear white colourless tissues, whereas 



the tissues placed in alcohol have invariably turned to aMirty 

 brown. 



In the same Journal, Prof. C. J. Chamberlain continues his 

 admirable series of articles on methods in plant histology. He 

 treats of the Algae, freshwater and marine, and of the Fungi 

 Under the Phyco- 

 mycetes, he briefly 

 discusses Mucor sto- 

 lonifer, the familiar 

 bread mould, and 

 suggests the follow- 

 ing method as a sure 

 and rapid method 

 for obtaining it: — 

 Place a glass tum- 

 bler in a plate of 

 water, put a slice 

 of bread on the 

 tumbler, and cover 

 with a glass jar. To 

 obtain such a series 

 as is shown on the 

 A-D of the figure, 

 the material should 

 be studied before 

 the sporangia begin to turn black. The phase in the life-liistory 

 indicated in F-H is rarely seen, and therefore the writer would 

 be glad to hear from anyone who has met this phase, especially if 

 the information could be accompanied by a few dry zygospores. 

 A very satisf actoi'y study may be made from the living material. 

 Corrosive sublimate (four per cent.) in fifty per cent, alcohol, 

 used hot, is recommended as a fixing agent. 



A-D. — Successive stages in the development of the sporangium. 

 E. — Columella with a few spores adhering. F-H. — Stages in 

 the formation of the zygospore. 



NOTES ON COMETS AND METEORS. 



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



Comets. — At present there is very little of general interest to 

 observers as regards visible comets. Several of these objects 

 may possibly be picked up in very large telescopes, but they 

 have passed beyond the capacity of ordinary instruments. 



The year 1899 has not been very productive of cometary 

 discoveries, for only two new comets h.ave been announced 

 These were by Lewis Swift on March 3rd, and by Giacobini on 

 September 29th. Apait from these, returns of three periodical 

 comets have been observed, viz., that of Holmes's comet (detected 

 by Perrine on June 10th, perihelion passage April 28th), 

 Tuttle's comet (detected by Wolf at Heidellierg, March 5th, 

 perihelion passage May 14th), and Tempel's comet, 1873 II. 

 (detected by Perrine, May 0th, perihelion jjassage September 

 28th). The first periodical comet due in 1900 will be Finlay's 

 (seen in 1886 and 1893), which should be in perihelion early in 

 the spring, but the conditions will be unfavourable, and the 

 comet may escape observation at this return. In the autumn 

 of 1906 this comet should be well seen, as it will be com- 

 paratively near the earth. 



Holmes's Comet. — Mr. R. G. Aitken, in describing (Asl. 

 Niicli. 3602) six observations which he obtained of this object 

 in August and September with the 36-inch equatorial of the 

 Lick Observatory, says " The comet was very faint — not as 

 bright as a 14th magnitude star when best seen — and on the 

 night of September 2nd, when the seeing was very poor, it was 

 at times entirely invisible. It showed only feeble condensation, 

 and the outlines were very vague." 



The Shower of Leonids in 1899. — A large number of 

 observers have reported observations, but the experience in 

 Enghand and foreign places seems to have been general that the 

 phenomenon presented a very feeble aspect. Occasional meteors 

 shot from the sickle of Leo, and demonstrated that the earth 

 was either passing near or through the swarm, but the brilliant 

 spectacle which it was hoped would have been visible was 

 nowhere realized. Many people who do not even make a hobby 

 of astronomy remained up all night watching from their windows 



