190 



KNOWLEDGE. 



[August 1, 1900. 



of which are a Wide Angle Immersion Condenser with an aperture 

 of 1.4 N.A., an aplanatic cone of 1.3 N.A., and a workinj; distance 

 of .06 of an inch. They have also introduced a new, cheap one- 

 tenth immersion objective, with an aperture of 1. N.A. 



The copper amalgam, kncjwn as Viennese metal cement, is 

 well adapted for modelling the most delicate objects, and it is 

 therefore of special value to the histological microscopist. The 

 method of preparation is as follows : Copper is precipitated as a 

 verj' fine powder from a solution of blue vitriol by means of strip* 

 of zinc, and after being washed and treated with a solution of 

 mercurous nitrate, hot water is poured over the copper in a mortar, 

 and the mercury, in the proportion of seven parts to three of copper, 

 is added. The resulting amalgam becomes so soft under water that 

 it can be used for modelling the most delicate objects from plaster 

 casts. It hardens into a malleable mass that can be polished like 

 gold and is not reailily tarnished except by hydrogen sulphide, and 

 it is a strong cement for metals. When impressions have been made 

 on thin sheets the amalgam may be reinforced by pouring on molten 

 type metal. 



The Bausch and Lomb Optical Company has just issued a revised 

 edition of a useful little manual entitled " Manipulation of the 

 Microscope." 



Corks that have been steeped in vaseline are an excellent sub- 

 stitute for glass stoppers without their disadvantages. They are 

 not affected by acids or chemical fumes, and they do not become 

 fixed by a blow or by long disuse. 



The "following process for preparing delicate specimens of hymen- 

 optera for mounting is strongly recommended. The in.sects are 

 placed in a wide-mouthed bottle containing an acid mixture made 

 up of one ounce of pure, dry crystals of carbolic acid dissolved in 

 four ounces of oil of turpentine, and are left to soak in this for a 

 couple of days. A specimen is then taken out and arranged on a 

 glass slip. A cover glass is placed over it, and sufficient pressure 

 applied to flatten out the thorax. It is then placed between clips 

 and allowed to stand in the acid solution for a day or two longer, 

 after which it is carefully washed in filtered oil of turpentine, again 

 placed between the clips and soaked in the turpentine for two or 

 three days. This hardens the insect so that it can be easily handled 

 without" breaking. It is now ready to be mounted in moderately 

 thin balsam. 



The classification of fresh-water sponges is based upon the form 

 and character of the spicules. As these are invisible to the naked 

 eye, and are difficult to obtain without special preparation, the 

 following method of development will be of interest to the student 

 and to the collector alike. The spicules are embedded in the 

 sarcode or flesh of the sponge, and the object of the processes of 

 preparation is to effectually remove this organic matter. To do 

 this place a fragment of the sponge skeleton and a few gemmules 

 in a watch glass and apply a drop of nitric acid. Boil, and repeat 

 the process until the sarcode and gemmule contents have dis- 

 appeared. Thoroughly wash with distilled water, and stand on one 

 side to allow of the spicules separating out. 



Mons. B. Renault holds bacteria to have been a most powerful 

 factor in the world's geological development. He believes thao 

 they transformed wood into coal, and that several species of the 

 fossilized bacteria have been discovered in coal by himself and 

 Professor C. E. Bertrand. 



Formaldehyde is well known to the microscopist as an inexpensive 

 and effective fixing agent. As a rule it is seldom used in solution 

 stronger than ten per cent, and then generally in conjunction with 

 mercuric chloride. The following formula has yielded very satis- 

 factory results for normal tissues, the material being killed and 

 fixed in the solution in from six to twelve hours. Formaldehyde 40 

 per cent, solution, 50 c.c. ; distilled water, 50 c.c. ; glacial acetic 

 acid, 5 c.c. After fixing the tissues are transferred to three grades of 

 alcohol, viz., 50 per cent., 75 per cent., and 95 per cent, respectively, 

 and mounted in paraffine. Care should be taken to perform the opera- 

 tion of dehydration thoroughly, otherwise the sections will drop 

 out of the embedding matrix when being cut. The tissue may be 

 run back through xylol into absolute alcohol, and left until every 

 trace of water is removed. If the specimen appears milky or 

 opaque in the clearing fluid it is not ready for embedding, but 

 needs to be left in alcohol for a longer time until dehydration is 

 complete. 



Beginners in microscopy frequently overlook the fact that it i? 

 possible to have the field of view too brilliantly illuminated. With 

 ordinary powers it is necessary, in order to secure good definition 

 of the finer details of the object, to moderate the brilliancy of the 

 light either by the use of the diaphragm attached to the sub-stage 

 or by moving the source of illumination further away. The result 

 of atoo brilliantly illuminated field of view is to " drown out " the 

 details and render the image flat, and therefore a clear, small light 

 is often a positive advantage. 



MoUuscan nerve tissues require careful treatment in the pre- 

 liminary stages of preparation to ensure satisfactory mounts. An 



effective macerating fluid for this purpose is prepared as follows : — 

 Acetic acid, 5 parts ; glycerine, 5 parts ; distilled water, 20 parts. 

 After sojiking the specimen.s in this for from four to twenty-four 

 hours they are teased in fifty per cent, glycerine, or washed and 

 stained in picro-carmine or ammonia-cannine. 



[All commu>i/catio7is in reference to this Column should be 

 addressed to Mr. J. 11. Cooke at the Office of Knowledge.] 



NOTES ON COMETS AND METEORS. 



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



Gi-'iCOBiNi's Comet. — This object is now rapidly becoming fainter, 

 with increasing distance from the earth. It will not be observable 

 during the second week of August owing to moonlight, but a 

 powerful telescope will reveal the object in the position assigned 

 by Berberich in the following ephemeris (Ast. Nach. 3636) : — 



Di.'^tance 

 Date. R.A. Declination. in Millions 



H. M.S. o / of Miles. 



August 3 ... 19 22 21 ... 39 51 N. ... 113 

 7 ... 18 57 55 ... 36 39 N. ... 117 

 15 ... 18 21 18 ... 30 7 N. ... 130 

 19 ... 18 8 ... 27 1 N. ... 137 

 „ 23 ... 17 57 19 ... 24 9 N. ... 146 

 27 ... 17 48 46 ... 21 30 N. ... 156 

 „ 31 ... 17 41 57 ... 19 5 N. ... 164 



Thus the comet's motion carries it rapidly through Lyra and 



Hercules. After August it will be an exceedingly faint object, and 

 only visible in very large instruments. 



Recent Cometart Discgvuries. — Very few new comets appeir 

 to have visited our parts of space during the last 15 months, judging 

 from the number of discoveries, for only two have been found, anrl 

 in both cases the first observer was M. Giacobini, of Nice. It is 

 true that several periodical comets have returned during the period 

 named, but on the whole comet seekers have met with very little 

 success. It is, however, highly probable that we shall shortly hear 

 of a discovery in this field, for the months of July and August have 

 been the most prolific hitherto in furnishing us with new comets. 



FiREB.iLL OF SuND.w, JuNE 10. — A large fireball was seen in the 

 twilight by several observers at widely distant stations. Lieut. -Col. 

 Boileau, M.D. , A. M.S., of Trowbridge, gave the time as about 

 9h. 10m., and described the meteor as passing about 15 degrees 

 above Venus from N.E. to W. at an angle of about 30 degrees. 

 Twilight was so strong that there was nothing visible in the 

 heavens except the moon, Venus, and Jupiter. At Spilsby, Lincoln, 

 the meteor was seen by Mr. J. Richardson, who says he first 

 noticed it about 60 degrees above the horizon like a shooting star 

 to the W.S.W. "After falling a few degrees at an angle of 75 

 degrees towards the S.W. it became very bright, and continued so 

 for about 30 degrees more, when it seemed to break into several 

 fragments and lose its light, finally diappearing rather suddenly 

 about 10 degrees above the horizon. It was 2 seconds in falling, 

 and appeared considerably more than double the diameter of 

 Jupiter." The Rev. F. B. Allison, of Peasmarsh, gives the time 

 as 9h. 12m., and says the first appearance was at some 10 degrees 

 altitude. The meteor then appeared to traverse a meridian (8h. 30m 

 about) and occupied 1^ seconds in passing over 10 degrees to a lo>v 

 cloud on the horizon behind which it dis,appeared. The brightness 

 of the head was 1^ times that of Venus. The meteor left a short 

 flaming tail of intense green colour, after which came a trail of 

 sparks of several degrees in length ; the meteor was slow. At 

 Colwyn Bay Mr. W. B. Russell noticed it falling in the southern 

 sky at 9h. 15m. p.m. The meteor was more than double the 

 diameter of Jupiter, and it fell perpendicularly downwards, leaving 

 a most brilliant copper green trail. Its course was very short. .\ 

 friend who was with Mr. Russell thought the colour at first blue 

 and green, and the nucleus of the meteor seemed to break into 

 two fragments. Mr. A. Mee, of Cardiff, saw the meteor in the west 

 about one-third of the way from the horizon to the zenith, but no 

 further particulars are given as to the direction of flight or velocity. 



Comparing the various accounts it appears highly probable that 

 the meteor was a Cepheid, and from a radiant eitlier at 336 + 73 

 or 310 + 77. The heights were from about 65 miles over Lampeter 

 to 28 miles over a point near Worm Head. Gower, S. Wales, but 

 these results are approximate, and more observations are required 

 before the meteor's exact path in the air can be determined. 



Large Meteors. — Mr. A. King, of Leicester, reports that on 

 June 24, at lOh. blifoa.., he saw a fine meteor of a beautiful yelloif 

 hue and brighter than Venus at maximum. The first part of the 

 flight was not weD seen, as the observer was not facing the object, 

 but the latter part of the course was from 213" + 444° to 203° + 22°, 



