Fkbbdary 1, 1900.] 



KNOWLEDGE, 



45 



winters. Those ten wint<?i-s show a total of 657 frost 

 days, being 107 over the average. 



In the ten-winter group about lSo6, seven out of the 

 ton were also severe; but the total excess was only GO. 

 At the minimum '73. we find six winters mild and four 

 severe (total deficiency 2S). 



Tliis pronounced peak of cold (about 1890), how is 

 it to be accounted for? Speculation seems vain, till we 

 know more about ocean currents, cosmic influences, and 

 other things. 



Then, there is the other crest of the curve in 1856; 

 and we may note the fact, that its distance from 1890 

 is just 34 years, reminding us of Bruckner's pei'iod, with 

 an average of 35 years. 



Once more, we find that in the sixties and seventies, 

 the cold of those ten-winter groups is generally slight, 

 while the X. and E. wind gives way to more genial 

 currents, and rain is abundant. A pi'ovalencc of 

 northerly wind, it may be noted, probably con-esj)onds 

 with frequent areas of high pressure in the west of 

 these islands, and a prevalence of easterly winds, with 

 high pressure systems in the north (the circulation in 

 such areas, in our hemisphei-e, being with the hands 

 of a watch). Many interesting points in the behaviour 

 of such systems have been lately brought out by 

 Van Bebber. 



E. Frost days in lieart of France, smoothed. F. Verj cold days, 

 Genera, smoothed. Gr. Frost days, Geneva, emoothed. 



It may be interesting if we turn for a moment to 

 look at the state of things on the Continent. E is the 

 curve derived from that of frost days in the heart of 

 Fi-ance (Pare ae Baleine), and G the same for Geneva 

 (with different scale) ; while F represents very cold 

 days at Geneva; days, viz., in which the thermometer 



did not rise beyond freezing point. All three arc 

 obtained in tlie same way as liefore, each point repre- 

 senting the average of ten years. These curves all show a 

 long trough between two high waves as before ; the later 

 waves in each case culminating about 1890 or 1891, 

 as in London; but the earlier wave somewhat earlier 

 than in the London curves. Furtlicr details may be 

 left for the consideration of the reader. 



Reverting to the London curves, do they throw any 

 light on the future! 



If we take the curve B as roughly representing 

 Braekner's period of 35 years, and accept his evidence 

 showing that this period may be traced back in one way 

 or another through about two centuries at least, we 

 might pei'haps rea,sonably look for some kind of repeti- 

 tion of the descent from 1856 to 1873 (i.e., 17 years), 

 bringing us to a minimum about 1907; this being 

 followed by a general rise to another maximum about 

 192-1. 



We are evidently now in a period of declining cold ; 

 and the decline in those averages has, so far, been 

 rapid. Wo can hardly suppose this decline will be 

 continuous (i.e., without temporaiy rise) to the supposed 

 minimum, nor is it likely to be so rapid as it has been 

 since 1890 ; and in any case it would be difficult to fix, in 

 advance, with much precision, the character of the in- 

 dividual winters covered by it. But at least it seems 

 probable that, for a good many years to come, wo shall 

 not be visited with such an accumulation of cold as 

 that in the ten vears about 1890. 



IHtcrosfopg. 



By JiMiN II. CodKi;, f.l.s., F.ri.s. 



MicuiiPiioToGR.M'HV is now used by microscopists so exten- 

 sively for educational, medical, and other professional pur- 

 poses, that we propose to incorporate in these columns notes on 

 new apparatus and methods dealing with this branch of micro- 

 scopy. We shall therefore be pleased to hear from readers 

 interested in the subject, and shall be glad to receive from them 

 notes of any improvised laboratory, apparatus, or devices in 

 manipulation that they may have adopted. Such ajiparatns and 

 devices are frequently of real practical v.alue, but being, perhaps, 

 obviou.sly simple to their originator, it does not occur to him 

 that they may be of use to his fellow-workers. 



Micro-photography is one of the simplest and best methods 

 known for making permanent records of microscopic studies. 

 It is not, however, so universally used as it should be, and this, 

 not .so much for the few difficulties that it offers, as on account 

 of the mistaken ideas as to the cost of the ajjparatus required. 

 Good work may be done by a patient and skilful manipulator 

 with an ordinary camera, or any other makeshift arrangement ; 

 but such good work would, in all probability, be rendered still 

 more valuable by the use of apparatus specially designed for 

 the work. The question of cost can no longer be considered 

 .seriously as an obstacle to its practice. 



There are now several makers who are prepared to sell well- 

 made cameras for photo-micrographic work at prices consider- 

 ably less than the cost of an ordinary camera. Messrs. Griffiths, 

 Highgate Square, Birmingham, have a particularly good appa- 

 ratus, consisting of a well-made bellows camera, extending from 

 twelve to thirty inches, and attached to a neat base, carrying 

 camera, microscope, and conden.sers. The object is readily 

 focussed in any position by means of a long, adjustable brass 

 rod which is attached to, and runs the %yhole length of the 

 camera, and which is connected with the milled head of the fine 

 adjustment screw of the micro.scope by means of a silk thread 

 passing over a grooved wheel at the end of the rod. It is made 

 in half-plate size with carriers for smaller-sized plates, and its 

 price places it wichin the reach of all. 



The photography of living bacteria and other cultures cannot 

 be successfully accomplished with a horizontal camera. ''''•» 



The 



