HA RD WICK& S SCTENCE- G OS SIP. 



hematoxylin to be, not in any reagents used in 

 preparing the specimens, but in the presence of 

 tannin in the ordinary hematoxylin stains. His 

 recipe for preparing the stain so as to get rid of the 

 tannin may be found in the " Quarterly Journal of 

 Microscopical Science," 1S85, at the end of an 

 article on the " Eyes of Insects." 



Perhaps tannin, chromates, acids, and turpentine 

 all contribute to make it fade. My own recipe is as 

 follows ; it gives as good results as any hematoxylin 



1 have ever seen ; but if fading be because of the 

 presence of the tannin in the logwood, my slides will 

 fade in time. 



Crush ordinary extract of logwood to powder, and 

 dissolve a saltspoonful of it in hot water ; add about 



2 oz. of methylated spirit ; dissolve a teaspoonful of 

 alum in some more hot water, and mix the two 

 solutions ; add more water (if necessary) until the 

 bulk equals three ounces. Allow the fluid to stand 

 for some hours ; then filter. Keep it a week before 

 you use it, and then filter it a second time. 



I have lately stained a few slides with " Carters'" 

 blue-black ink, diluted with water and spirits. It 

 gives very good results, and colours specimens either 

 a pleasant blue-black, or (if you leave the slide a 

 couple of hours in water or spirit after staining), a 

 gray, like the tone of a photogravure. The definition 

 is not quite so sharp as that given by hematoxylin, 

 but I have a retina of a spider excellently well stained 

 by it. As I have only used it for a very short time, 

 I should not venture to recommend it as anything 

 very first-rate, but I think it decidedly worth trying. 

 On the other hand, nothing can beat hematoxylin 

 if it will only not fade. 



I keep my fluids— turpentine, spirits, and the 

 stains — in three-ounce, wide-mouthed, corked bottles. 

 These are tall enough, and the mouths wide enough 

 to take a slide. And so, by dipping the slides first 

 in the one bottle, then in another, as required, the 

 trouble of mounting is greatly reduced. It is a clean 

 process ; there is no waste ; and yet you always have 

 ample quantities of fluids. If you have two bottle- 

 fuls of each kind in use, you can have six or eight 

 slides in the course of preparation at once. 



In conclusion, a hint or two as to the sort of 

 insects to choose for cutting into sections will not be 

 amiss. Those with hard chitine should be avoided, 

 for, not only do their shells notch the razor terribly, 

 but they also crush into the softer parts while the 

 section is being cut, and so spoil it. Small insects 

 are much more easily cut than large ; long and cross 

 sections of whole insects are very instructive. Eyes 

 are very interesting, and spiders are particularly good 

 subjects. And, as comparatively little has been done 

 in " sectionising " insects as yet, there is room for 

 the enthusiastic entomologist to discover new facts, 

 and so do a little original work. 



Oxford. 



FORMS OF CLOUD IN RELATION TO 

 THEIR COMPONENT PARTICLES. 



: w E :: 



7"E shall have stormy weather, sir ; those 

 imal clouds have been about again to- 



day." Such was the remark made to me by a 

 country woman in Kent, and this observation was 

 true enough to nature : it agreed also with my own 

 notes at the time on the appearance of "Anvil cloud,' 

 oxfracto-cumulus. The " Ram's-head" cloud might 

 not inappropriately be the term used to describe this 

 drifting bank of hail or rain, which often marks the 

 sky with such striking and fantastic outlines. Observe 

 these dark rolling masses at sunset on an autumn 

 afternoon, and see what kind of weather the night 

 brings with it— driving sleet, and sudden gust of 

 wind, with "bursts " of hail rising often to a furious 

 and full-blown nor'wester, such as makes one thankful 

 for a good roof overhead. 



The general form and type of the "Hail cloud" 

 is pretty well known to observers of atmospheric 

 phenomena. In most cases it greatly resembles the 

 snow-cumulus, though generally more craggy in 

 outline, harder in its edges, and more attended by 

 stratus * at its base. There are, however, several types 

 of snow-cloud. When drifting against a clear sky, 

 the latter presents a more fleecy and softer edging, 

 though in its general form it must be grouped, like 

 that which originates hail-showers, with the class of 

 "Animal" cloud, i.e. condensed t Fracto-cumuhis. 

 Both of these are again closely akin to the Electric 

 cumulus, or Cone-cloud (see Science-Gossip for 

 July, 1879). This is natural enough when we recollect 

 the frequent connection existing between the hail- 

 shower and electrical discharges, and the part that 

 electricity is known to play in the condensation 

 and cohesion of the watery particles. 



Let us notice now that a "law" seems to hold 

 good in regard to the origin of the different forms of 

 cloud, and that this law is the real principle by virtue 

 of which it is possible to forecast weather from the 

 observation of clouds. This relation, which we may 

 term a "law of correspondence," between the 

 particles composing a cloud and the general form of 

 the mass, varies its manifestations with the tem- 

 perature and other physical conditions of the medium 

 in which the vapoury particles are floating : yet the 

 principle involved in the connection between the form 

 of the body and the molecules which compose it is 



constant. 



It is a physical or chemical question to deter- 

 mine the special forms that will be originated by 

 given component particles under given physical con- 

 ditions. To determine such resultant forms, in the 

 case of previously unknown substances, is a problem 



* This indicates a closer affinity with the rain cloud or 



n "f This is the term adopted by Professor Po'ey, and indicates 

 a mass broken by wind. 



