214 



KNOWLEDGE. 



[Septembek 1, 1899. 



•241J° + 230 to 218|° + 25" when it exploded, and finaUy 

 became extinct in 208° + 22^°. The path, carried far back in 

 the same direction, brings us to the radiant of the .July- August 

 Aquarids, and there is little doubt that this brilliant meteor 

 derived its oriffin from that well-known stream. 



By John H. Cooke, f.l.s., f.g.s. 



Canada balsam, one of the most useful of resinous media, is 

 usually slightly acid. In some cases this is a drawback, but for 

 mounting sections stained vrith carmine, or injected with 

 carmine gelatine, or Berlin blue gelatine, it is advantageous. 

 The balsam may be neutralized by mixing a little carbonate of 

 soda with the thinned solution before it is thickened. The soda 

 settles after a few days and leaves the balsam clear and neutral. 

 Carmine will diffuse, and blue will fade in the neutral balsam. 



Thin mica plates are suggested as making good covers for 

 such objects as fish's eggs, frog's eggs, &c. On account of the 

 flexibility of the mica, the egg is less liable to be crushed than 

 with a glass cover, and if the effects of pressure on the develop- 

 ment of the egg are to he studied, the mica cover may be easily 

 manipulated. 



The preparation of a bone section so as to show the lacunse, 

 canaliculi and deep seated cells, may be qmckly effected by the 

 following method : — Take a fresh bone, and with a strong, 

 sharp knife cut off a thin shaving. Immerse the section in 

 carmine dissolved in ammonia, the ammonia being first neutra- 

 lized by acetic acid. The walls of the vessels which penetrate 

 the lacunas and canaliculi are by this means stained crimson, 

 and the true structure of the bone is thus rendered visible. 



A solution of gum-dammar in xylol is more suitable than 

 Canada balsam as a mounting medium for rock sections. 



To render micro-photographs self-luminous soak them in 

 castor-oil to make them transparent, and dust them over with 

 powdered sulphate of baryta or sulphite of lime. When dry 

 mount them on cardboard of a suitable .size with starch paste. 

 The phosphorescence of the salt lights up the photograph. 



Drying oils in every form, such as gold size, paint, etc., 

 becomes hard by oxidation, and not, as is generally supposed, 

 by evaporation. The drying process is frequently a long one. 

 Where time is an object, as in class demonstrations, it may be 

 expedited b}' placing the slides in a small chamber (a porcelain 

 dish answers admirably) and passing over them a stream of 

 oxygen obtained by the decomposition of potassium chlorate. 



A saturated solution of bichloride of mercury, to which has 

 been added one per cent, acetic is an excellent medium for 

 killing specimens of the protozoa on the slide or cover prepara- 

 tory to mounting. In some cases a hot solution is useful, as 

 being more rapid in its results, and producing little or no 

 deformity of the cells. 



It is a pity that amateur microscopists do not more fully 

 recognize the necessity of recording, to some uniform and con- 

 venient scale, the dimensions of the microscopic objects that 

 they make their study. This want of uniformity not only 

 detracts from the value of the work done, but it also renders 

 the work of comparison of the drawings of the objects laborious 

 and unreliable. By operating on some object of known size it 

 is easj' to ascertain what arrangement of the microscope, and of 

 its objectives and ocular, is necessary to obtain an image with 

 the camera lucida of any required size. Having determined on 

 a given amplification it should be adhered to, and a scale be 

 made corresponding to this amplification. The actual dimen- 

 sions of the object might then be readily ascertained by 

 appljing this scale to the various parts of the image or drawing. 

 The "value of some such uniform method as this is self evident. 



To prevent sand grains and other loose objects from being 

 forced out from under the cover-glass when mounting, Mr. H. C. 

 Sorby recommends that the objects should be well mixed with 

 weak gum and water, the gum to be of such a consistency as to 

 make it easy to separate the grains and spread them uniformly 

 over the space which will afterwards be covered by the cover- 

 "lass. The water is then allowed to evaporate slowlj*. Much 

 of the gum may collect around the margin, but by properly 

 regulating the quantity originally added, enough will remain 



under the laj-ger grains to hold them so fast that they will not 

 be squeezed out in the excess of balsam. 



Dr. !Marpmann, of Leipsic, has recently published the results 

 of his microscopical exarainations of sixty-seven samples of ink 

 used in schools. Most of these inks were made with gall nuts, 

 and contained saprophytes, bacteria, and micrococci. Xigrosin 

 ink taken from a freshly opened bottle was found to contain 

 both saprophytes and bacteria. Red and blue inks also yielded 

 numerous bacteria. In two instances he succeeded in cultivating 

 from nigrosin ink a baciUus which proved fatal to mice in four 

 days. This ink had stood in an open bottle for three months, 

 and the inference to be drawn from the enquiry is that ink used 

 in schools should always be kept covered when not in use. 



The current issue of the Ti-attsactioiis of the American 

 ^[icrof^copical Society contains inter alia a valuable article on 

 " Freshwater Investigations during the Last Five Tears," by 

 Dr. H. B. Ward, of Nebraska. It includes a bibliography of 

 every article, however small, that has been published on plankton 

 work since 1893, and it is therefore of great practical value to 

 those who have taken up this field of work. 



In the same publication. Dr. T. E. Oertel describes a con- 

 venient method for preparing nucleated blood in bulk for class 

 demonstration. No book on microscopical technique has given 

 details of preparing blood so as to yield absolute uniformity in 

 results. " Smears " are not as a rule satisfactory by reason of 

 the agglutination or crenation of the corpuscles, excess of serum, 

 and the formation of fibrin. Dr. Oertel's contribution is there- 

 fore of considerable practical value, inasmuch as it obviates all 

 of these defects. His method is, briefly, as follows : — Select a 

 large frog, chloroform it, open the thorax, puncture the aorta 

 and allow the blood to flow directly into a small glass jar con- 

 taining a one per cent, aqueous solution of osmic acid in the 

 proportion of one of blood to fifty of the solution. Allow the 

 cells to settle, decant the supernatant fluid and add distilled 

 water. Repeat this process, after which add Bohmer's hasma- 

 toxylin diluted one-half with distilled water. After a few 

 moments' staining, filter ; wash filtrate from the paper and 

 pass through the various grades of alcohol, beginning with 

 seventy per cent, and finishing with absolute. Clear in carbol- 

 xylol, and after drawing off as much of the liquid as possible 

 add thin xylol balsam. Keep in a well-stoppered bottle, and 

 when required for use transfer a drop with a glass rod to the 

 slide, and super-impose a cover-glass. A neat and permanent 

 preparation is the result. 



THE FACE OF THE SKY FOR SEPTEMBER. 



By A. Fowler, f.r.a.s. 



THE SUN.— On the 1st the Sun rises at 5.14, and 

 sets at 6.46 ; on the 30th he rises at 6.0, and 

 sets at 5.40. He enters Libra, and autumm 

 commences, at 6 o'clock on the morning of the 

 23rd. 

 The Moon.— The Moon will be new on the 5th, at 3.33 

 A.M.; enter first quarter on the 12th, at 9.49 p.m. ; will be 

 full on the 19th, at 12.31 p.m. ; and enter last quarter 

 on the 26th, at 3.3 p.m. Two or three days before and 

 after full the Moon rises nearly at the same time, thus 

 giving us the well-known phenomena of the Harvest Moon. 

 The sixth magnitude star, 39 Ophiuchi, will be 

 occulted on the 12th ; the disappearance will take place 

 at 8.47 P.M., at 28= from the north point (2= from the 

 vertex), and the reappearance at 9.26 p.m., at 318° from the 

 north point (287° from the vertex). The Moon sets at 

 9.33 P.M. 



The Planets. — Mercury is a morning star throughout 

 the month, and during the first part is very well placed 

 for observation. He will be at greatest westerly elongation 

 at 7 A.M. on the 5th, but as the planet is at perihelion on 

 the 9th, the angular distance from the Sun only amounts 

 to 18' 2'. Still, the apparition is specially favourable for our 

 latitudes because of the great inclination of the ecliptic 

 to the horizon near the time of sunrise at this time of the 



