238 



KNOWLEDGE. 



[October 1, 1900. 



the soil, enrich it by axiding to it such compounds of 

 Nitrogen, and thereby render it more fertile the next 

 season for a crop which possesses no means of iitUising 

 the free Nitrogen of the air. 



♦ 



NOTES ON COMETS AND METEORS. 



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



Borrellt-Brooks's Comet. — This object has formed a very 

 interesting one for telescopic observers during the last two months. 

 It has exhibited a well defined tail and bright head ; in fact its 

 aspect lias been that of a large comet presented in miniature. Its 

 motion away from the earth and sun has now rendered it extremely 

 faint, and it will soon pass beyond the range of the most powerful 

 telescopes. At the beginning of October the position of the comet 

 is 5 degrees S.W. of the stars (i — 7 Ursac Minoris, and its 

 motion is directed towards the S.E., but it is now apparently travel- 

 ling very slowly. A very large number of observations of this object 

 have been obtained at observatories in various parts of the world. 

 Its orbit appears to be parabolic, but definite elements have not 

 yet been computed. 



Barnard's Comet (1884 II.).— In Ast. Nach. 3660, A. Berberich 

 gives a sweeping ephemeris of this object. Its perihelion passage 

 wall probably take place at the end of October, but the precise 

 date is uncertain. On October 23 the computed place of the 

 comet will be E.A. 17h. :Uin., Dec. - 27" 12', but its southerly 

 position and great distance (nearly 150 millions of miles) from the 

 earth must prevent its being seen in this country except in a very 

 powerful telescope. The comet was discovered in 1884, and has 

 a period of about Sj j'ears. It must have returned to perihelion in 

 1890 and 1895, but escaped observation on both occasions. It seems 

 probable that, in view of the unfavourable conditions, the comet 

 will again elude detection during its present return. 



Fireballs. — A considerable number of these objects have been 

 reported from various places during the past two months. In the 

 majority of cases, however, the observations are not sufficiently 

 full and accurate to enable the real paths of the meteors to be 

 computed. On July 30. at lOh. 46m., a very brilliant Perseid was 

 seen from the S.W. part of England and from Jersey. It fell from 

 a height of about 95 to 50 miles over the English Channel, S. of 

 Cornwall. On August 19, several brilliant fireballs appeared in the 

 moonlight. Two are described by the Rev. T. E. R. PhiUips of 

 Yeovil. One of these was seen at lOh. 21m., and was brighter 

 than Venus. It travelled from 2914 ■ + 30" to 271" - 7", and was 

 a fine Perseid. The other came two minutes later, and shot from 

 252" + 2-i" to 19.^° + 59", and was probably directed from the same 

 radiant as the fireball of July 21. at 2S(r - 15\ On August 19, 

 lOh. 36m., the end point of a brilliant fireball was observed by the 

 writer at Bristol at 198" + 2(i", and the same object was seen at 

 Yeovil by the Rev. T. E. R. PhiUips, and at places in Ireland by 

 other observers. Its radiant point was at 3-16" + 1", and it de- 

 scended from 56 to 29 miles over the east coast of Ireland, but 

 only the latter portion of the flight seems to have been satisfactorily 

 recorded. When the fireball first became visibly incandescent it 

 was probably much higher than 56 miles, and it is hoped that 

 further observations of it will come to hand. On August 22, 

 lOh. 8m., a fine meteor estimated equal to Jupiter was seen by 

 Mr. A. King at Leicester, and by the writer at Bristol. It proves 

 to have been a Cygnid from a radiant at 310" -^ 53' , and having 

 heights of 75 to 50 miles. 



Large D.wlioht Meteor of September 2. — Just before sunset 

 on September 2 at 6h. 54m. a magnificent meteor was seen from 

 the northern crmnties of England and from Scotland. A consider- 

 able cumber of descrijitions have appeared in the newspapers, and 

 Mr. W. H. S. Mnnck, of Dublin, has collected and kindly furnished 

 me with many of these. The meteor appeared at a time when there 

 were no stars or planets visible by which to mark its apparent path, 

 hence the accounts give positions which were only roughly estimated. 

 A full discussion of the materials has not yet been attempted, 

 but it appears certain that the meteor disappeared over Lancashire 

 at a height between 20 and 25 miles, and that it was directed from 

 a radiant probably in Cepheus at 33-1" -i- 57 ". At Bristol 5 meteors 

 were observed from the shower later on the same night but they 

 were small. The faintest meteors and the largest fireballs are, 

 however, directed from the same radiant points. 



August Shooting Stars. — The full moon of August 10 practically 

 obliterated the Perseids at and near the time of maximum display 

 this year, but a few ot the usual streak-leaving meteors of this 

 prominent system were noticed at various places. They appear 

 to have been most numerous on the veiy clear night of August 12. 

 The change in the position of the radiant was noticed by several 

 observers. At Bristol, between August 16 and 26, in watches 

 extending in the aggregate over 15 hours, 125 meteors were 



observed. The chief shower was at 346+1° (12 meteors), and 

 there was another active radiant at 333" -I- 28" (11 meteors). The 

 Perseids still exhibited striking activity on August 16, and indicated 

 a radiant at 5-1" f 58". On August 22 about 5 streak-leaving 

 meteors gave a good centre at 59" + 59", which is close to the 

 computed place of the Perseid radiant, but there is a shower of 

 Oamelopardids from this point, and it is possible that the meteors 

 were not real Perseids. The observations are, however, very signifi- 

 cant that the Perseid shower continues until August 22. This was 

 distinctly suggested by Lieut. -Col. Tupman's observations in the 

 Mediteiranean in 1870, but I recognised very little if any evidences 

 of the prolongation of the shower on August 22 in the years 1879, 

 1884, and 1887, when I registered a considerable number of meteors 

 on this date. The point is an interesting one. It will be important 

 to learn in future years the visible strength of the shower on the 

 nights intervening between August 16 and 22. The radiant is 

 very well defined on {]■' former date, but before assuming that it 

 continues in action to the 22nd we must thoroughly watch for it 

 on the immediately previous nights, and this will enable us to assign 

 definite limits to the showers' sustenance. From the writer's own 

 observations at Bristol there can be no doubt that Perseids continue 

 to fall as late as August 19, but the Perseid-like meteors seen on 

 following nights may belong to a distinct shower in Oamelopardus, 

 very well defined earlier in the month, and notably on Augu'st 

 16 :it tlie point 61" -t- 6(1". 



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



Mr. G. H. J. Rogers, f.e.m.s., has invented an improved form 

 of compressor for which the principal advantage claimed is the 

 ready replacement of the cover glass in the event of it being broken 

 by accident. 



Chinese cement is composed of finely powdered calcined lime 54 

 parts, alum 6 parts, fresh blood 40 parts. These are worked into 

 a homogeneous mass. Pasteboard saturated with it will become 

 as hard as wood. 



One of the diSiculties experienced by those who keep fresh water 

 aquaria for the purpose of cultivating material for microscopical 

 study or class work is the rapid decay of the plants, due in a 

 measure to the ravages of the bacterial zooglcea that form on the 

 surface of the water. To prevent this, the water must be supplied 

 with oxygen by growing in it some good aerating plants like 

 Myiiophyllum, Cabomba, Ranunculus, water mosses, etc. Algae 

 like Vaucheria, Spirogyra, Cliara, Nitella, Coleochaeta, Oedogonium, 

 will thrive and fruit provided that the conditions are suitable. 

 Where the aerating plants themselves do not thrive algae may be 

 successfully cultivated, provided that means be adopted to protect 

 the surface of the water so as to exclude dust, but permit free access 

 of air. If the aquaria are small, this may be readily effected by 

 covering them T\ith loose glass covers ; but, where they are large, 

 a better method is to encourage the growth of the floating plant 

 Salvinia nutans, which propagates rapidly and protects the surface 

 from the accumulation of bacterial zooglosa. Plants such as 

 Azolla or Lemna would perform the same functions, but both of 

 these have their periods of decay when they disappear altogether, 

 while the Salvinia is in evidence all .the year round. 



A supply of fruiting Vaucheria may be obtained at any time of 

 the year by carefully removing the mats from pots in greenhouses, 

 and throwing them into a jar half full of water. The jar should 

 be placed in .strong sunlight, and in five or six weeks the material 

 may show both methods of reproduction and will be practically free 

 from dirt and other algte. 



Fresh water rhizopods are more common in the ordinary col- 

 lections of the microscopists than is generally supposed, but since 

 they are seldom looked for they are often passed bj' unnoticed. In 

 systematic collections the superficial ooze at the bottom of still 

 water should be examined, after it has been allowed to settle for 

 some time in a suitable vessel. Rhizopods are common in the sUme 

 of submerged rocks, stems, and leaves, especially so in moist 

 Sphagnum ; they are to be found almost everywhere in moist 

 situations not too much shaded, among decaying logs, mosses, 

 lichens, and on the bark of trees. 



The motion of camphor in water is well known. A German 

 chemist, K. Schaum, has taken such readily soluble substances as 

 potassium cyanide, potassium nitrate, silver nitrate, calcium 

 chloride, and sugar, and has studied their travels in dissolving with 

 the aid of the microscope by dropping single crystals upon mercury 

 covered by water or dilute acid. The movements — greater in dilute 

 acid than water — are very ch.-racteristic. The crystal first takes 

 a zigzag course, then changes to a circular path, and finally turns 

 rapidly on its axis. The rate of motion varies with the rate ot 

 solution and the surface tension of the mercury. 



