126 



KNOWLEDGE. 



April. \9\\. 



to a point ht-low that of thu untn-'atcd 

 Many different species of soil proto;^o 



lieen isolatecj. chief amonj; 



which ma\- be mentioned 



P 1 e u r o t r i c h a . C o 1 p o d a . 



\'orticelhds. Amoebae, and 



Monads. A large number of 



soils ha\-e been examined, 



and these organisms would 



appear to be of uni\ersal 



occurrence : tlu ir nuniber 



varies \\ith different soils. 



and at different de[iths of 



the same soil. 



A study of their beha\'iour 



towards \'arious ph}'sical 



and chemical agents has sug- 

 gested fresh lines for investi- 

 gation in connection \\itli 



soil tcrtilit}-. Experiments 



ha\e shown the thermal 



death-point of protozoa to 



lie between 4J" and 4<S" f. 



and it has been found that if 



a soil be heated to 50" C. 



instead of fOO" C, as for- 

 merly, a change occurs 



similar to that i>roduced b\ 



toluene. The relatit)ns of 



protozoa to intense col<l 



or thorough desiccation are 



still being in\-estigated. It 



is commonh- belie\'ed b\ 



practical agriculturists that 



a sharp hard frost conduces 



to increased crop j)roduction 



soil bacteria, 

 a have alread\- 



Figure J. 



■ri)iii a Plmtii-Micrograph I Plcinutricha, one of the 

 Protozoa occurring in Soil I. 



and in the light of the aboN'e results it would appear 

 to lie justilied. as extreme cold for a short period 



is sufficient to kill main' 

 protozoa. The Indian prac- 

 tice of cultiwating and 

 pulverising the soil during 

 the hot tlr\- season would 

 appear to rest upon a similar 

 foundation. 



In this countr\- where 

 extremes of cold, heat, or 

 dryness scarcely ever prevail 

 for any considerable period, 

 any effectual method of 

 partially sterilising the soil 

 would necessitate the use of 

 cheap antiseptics or the 

 ajiplication of tempera- 

 tures easily obtained in 

 market gardens and glass 

 houses. 



\Miate\'er success mav be 

 gained in the adoption of 

 the methods of partial 

 sterilisation on a large scale, 

 it becomes evident from the 

 above results, that a fresli 

 factor must be recognised in 

 the estimation of soil fertilit\-. 

 In the meantime much work 

 remains to be done in the 

 study of the relations ex- 

 isting between bacteria and 

 protozoa and the conditions 



govermn£ 

 the soil. 



tht 



.rrowth m 



M I'Ti: oRK" A,S r KOXOM \- 



1!\- W. I-. DENNING, F.R.A.S. 



Tm. claims of meteoric astronomy as an attractive field of 

 ohscrvation, and as a subject of investigation likely to expand 

 our l<no\vledge, are great — yet it must be cunfesscd tliat it is 

 not studied as it should be. 



A large amount of useful worl< was accomplished by the 

 British Association Committee on luminous meteors, between 

 1848 and fSSO, and certain individuals ha\c contributed a 

 considerable amount of data to this department, but much more 

 remains to be done. The southern skv is still practically 

 unexplored. 



Meteors not only iieiineate our solar system but probably 

 circulate far outside that and may indeed pervade tlie whole 

 universe of stars. If the latter are suns with planetary 

 satellites then fragmentary atoms probablv abound, some 

 in the form of cometary swarms, others in more tenuous 

 streams. In fact, \vhere\cr iilanelary systt'Uis exist we 

 may take it that meteoric particles, forming as it were 

 the dusi of such systems, are also puscnl in con- 

 siderable numbers. And across the wide ami incompre- 

 hensible .abyss separating one sun from another nu'teors mav 

 roam in hyperbolic or p.arabolic orbits. The lar-reaching 

 rel.ations of these objects, their vast numbc i>, ,uid conietarv 



associations rende.- them of extreme interest and importance. 

 We must learn more' of the phenomena which they present in 

 our terrestrial skies, so that we may judge of their character 

 and behaviour in the remoter regions of space. 



For the present it seems that the photography of meteors 

 has failed to supply us with an effective and accurate means 

 of recording their flights on ordinary nights of the year. We 

 must continue therefore to follow the old and rough method of 

 registering paths and determining radiants. When we con- 

 sider. howe\er, that radiation forms an area not a point, and 

 that eye-estimates of the directions of flight may, after 

 sufficient practice, be made with a precision almost equal to 

 photographic trials, the latter has really only a slight advantage. 



The chief periodical showers of the j-ear have been watched 

 for many years, and a large amount of e\idence concerning 

 their displays has been accumulated. Still the materials 

 existing are far from being of the character or extent recpiircd. 

 We w.int nirire data as regards the long duration of showers 

 .ind as to their stationary or shifting positions of radiation. 

 The r.idiant points of the principal streams should be 

 determined on ten or more nights near the date of maxi- 

 nnnn in cases where the showers are active so long as that. 



