196 



KNOWLEDGE, 



[SePTEMHKB, 1902. 



on the roiindi'd part outside, and it is sure to 1)0 found 

 wlicrover the thistle occurs. Thou^'li it is a very ]ir('tty 

 insect, and will fjive a good idea of what a liice-buj,' is 

 like j,'t'nerally, it is neither so elegant nor so (|ii:iint in 

 form as the little Derephyiiia describtnl above. 



For our last oddity in the |iresent paper, we uiiist go to 

 a weeily ])ond, and search 

 for the littli; water-bug 

 called Plea minutiniiima 

 (Fig. tj). We pull out 

 a mass of the water weeds, 

 and s])read them out on a 

 piece of macintosh. We 

 soon notice some little fat 

 whitish bodies moving 

 slowly about amongst the 

 weeds ; these are the ob- 

 jects of which we are in 

 search, though they do not at first sight seem to 

 be insects at all. If we separate one of them from 

 the wet mass, let it dry itself, and bring a hand lens 

 to bear upon it, we find it is really a six-legged being, and 

 therefore an insect, though its legs are not very noticeable, 

 as they are kept near the body and are of the same pale 

 colour. It has a. head as broad as the body, with two 

 large masses of eyes at the sides, and a very humped back, 

 which descends almost perpendicularly behind, making 

 the little being look like a very sh(nt and tubby inverted 

 boat. Very close scrutiny will reveal a sloping line on the 

 visible wings, dividing their area into two ])arts, the 

 clavus and corium of the ordinary bug type. Turning it 

 over on its back, we note the little beak, which confirms 

 the indications of the wings, that it is a Hemipteron. The 

 whole surface is indented with little pits, as though it were 

 grievously pock-marked. This odd little being is a near 

 relative of the water boatman, and often occurs by hundreds 

 in our ponds, where it lives an uneventful life amongst 

 the weeds. 



Thus all the oddities we have considered in this paper 

 belong to the one order Rhyuchota, or Hemiptera, in either 

 one or other of its sections, the Heteroptera, or bugs proper, 

 and the Homoptera, or frog-hoppers. In our next paper 

 we sliall consider some oddities belonging to other orders. 



THE AIR OVER LONDON. 



By the Eev. John M. Bacon. 

 As long ago as 1842, John Wise, of America, made an 

 important statement respecting general upper currents 

 which I believe will be fairly universally accepted at the 

 present day. Wise adopted the career of a professional 

 aeronaut, starting with no previous training, and there 

 being no experts at that time in his own country his 

 investigations and deductions were from the beginning 

 wholly independent. He built his experimental balloon 

 of mere longcloth, invented his own varnish, and, step by 

 step, collected his facts with intelligent diligeu<'e not to 

 be surj)assed. At the end of a career of many years he 

 convinced himself of the possibility of crossing the 

 Atlantic in a balloon of adequate size, and apjdied to 

 Congress for funds to make the attempt, stating in his 

 own words : — " It is now beyond a doubt in my mind 

 established that a current from west to east in the 

 atmosphere is constantly in motion within the height of 

 12,000 ft. above the ocean." 



I have always looked upon this as a very valuable, 

 practical and independent confirmation of the theory with 

 which we are now familiar, namely, that somewhere, and 

 as it would seem at an accessible height, there is a general 



air stre.am in our latitudes following the direction of thr- 

 earth's rotation. It is to this general and moderately 

 lofty iipjier west wind that, in my opinion, we must refer 

 certain important conditions which can be readily noted 

 by the man in the street with regard to the air above 

 fjondon. 



It would seem a common rule that when contrary lower 

 winds meet and mingle with this upper current the air 

 aloft grows hazy, robbing direct sunlight of much of its 

 intensity ; while, on the other hand, with lower westerly 

 winds Londoners may look for their clearest air, and this 

 not only for the above reas<m but also because of the 

 blowing away from London ]>roper of the smoke of the 

 city. As to the dissipation of smoke I shall have a word 

 to add presently. However, with regard to a certain 

 condition of exceptional clearness over the east side of 

 London, it has been stated as the result of long-continued 

 obs(,'rvution at Greenwich, that whereas over and beyond 

 the river to the N. and N.N.E. there is usually hazy distance, 

 this haze is occasionally replaced by remarkable clearness, 

 at which times rain is the invariable consequence before the 

 next morning. Under such circumstances we cannot 

 suppose the clearness to be attril)utal)le to west winds, 

 which, as some meteorologists maintain, by their nioistui'e 

 cause absorbent dust particles to become too heavy to 

 remain in suspension ; for west currents in the pri'sent 

 case would assuredly bring with them smnke clouds 

 gathered from all London. 



It would be interesting to investigate what would be 

 the nature of the air if analysed at a time when great 

 visibility is manifest, at the average height at which haze 

 is usually detected; and here I am able to give a few 

 results gathered when chances have afforded me the 

 opportunity. Such chances are of course rare, for, in the 

 first place, the occasions when a balloon voyage can be 

 made fairly over London are infrequent, and the whole 

 period of a flight ovei'head being limited it may well 

 happen that the short time at disposal may have to be 

 devoted largely to other matters. 



Three times, however, during last summer I sailed 

 directly and leisurely over London, at moderate but varying 

 heights, when I was able to make observations both as to 

 haze and also as to palpable dust in suspension ; while I have 

 made many similar observations from some of the highest 

 accessible buildings. I would first call attention to the 

 fact that a series of photographs makes evident — what 

 indeed was patent to the eye — that haze, as viewed from 

 aloft, hung persistently over certain quarters, such haze 

 having no reference to the angle of illumination. For 

 example, in an aerial travel at about four thousand feet 

 altitude over the heart of London from the south-west to 

 the north-east, keeping the eye always S. and S.E., at the 

 start the river at Chelsea and the Surrey shore were per- 

 fectly clear, as in due course were also Trafalgar Square 

 and Westminster, and again later, remarkably so, the 

 region east of London Bridge. But over St. Paul's, 

 Blackfriars, and as far as Southwark Bridge, a thick haze 

 prevailed. In the next place, photographs from lofty 

 buildings show how on miiny occasions a haze which 

 blotted out the town late in the evening, and again early 

 the following morning, was strikingly aVisent through 

 night hours. The illustration given affords an example of 

 this. It was taken during a January night, and shows 

 great clearness of at inospliere, whereas from similar, as 

 also from lesser heights, photograjihs taken the afteruixm 

 before and the forenoon following showed no definition 

 whatever. 



With regard to dust in suspension over the town, my 

 observations go to show that in calm weather this will 

 hang at certain levels in strata, or, as I am led to believe, 



