398 



♦ KNOWLEDGE ♦ 



[Nov. 14, 1884. 



such an elaborate and complicated feeding machine ? 

 Does anybody know 1 The writer confesses complete 

 ignorance, and will not venture a guess. Books are so 

 generally mere compilations, one from another, that it is 

 little wonder that those ordinarily accessible contain no 

 account of this organ ; but it is curious that its complex 

 structure seems to have escaped Westwood at the date 

 (1840) of his excellent " Clas-sification of Insects." From 

 his sketch it is evident he had only seen the tongue with a 

 very low power. Figuier, in his " Insect World," says of 

 the Tipulce : — " The perfect insects, at first sight, resemble 

 gnats ; but are without a trunk, or rather their trunk is 

 extremely short, terminating in two large lips. The sucker 

 is composed of two fibres only." Where did he get this 

 notion 1 If any reader has met with a good description of 

 this tongue I should be glad to know of it. 



A curious question arises with respect to an organ of 

 this character in reference to the theory of development : 

 What did the ancestors of the present creatures do while 

 the thing was developing f A comparison of the mouth- 

 organs of various dipters may throw light upon the Daddy- 

 Longlegs case. The Tabani (breeze-flies) and others have, 

 besides the proboscis, piercing and cutting tools and a 

 pump. If in any insect the latter became gradually ob- 

 solete or imperfect while the former was growing, no incon- 

 venience would arise. The gnats are piercers and pumpers ; 

 smd perhaps remote progenitors of Daddy-Longlegs had 

 as good lancets, saws, and pumps, while the proboscis 

 passed from simple stages to the marvellous development 

 of the Tipula. Fig. 4 shows the tongue of Kliingias 

 rostrata, like dentist's forceps, with few and very short 

 lateral tracheae, and if we could find an early ancestor of 

 the Daddy, his proboscis might afford still simpler exhibi- 

 tion of this kind of organ. 



With regard to my paper on the Drone-flies, let me 

 thank Mr. John Moore for his kind ofier, and his remark 

 that their food is not exclusively liquid, as he finds pollen 

 in their stomachs. I have no doubt he is right, but 

 their regular diet is, I think, obtained by sucking the 

 nectar of florets, and I have examined many which had 

 not swallowed pollen or other solid matter. 



NOTES ON COAL. 



By Richard A. Proctor. 



(Continued from p. 334.) 



IN all such progressions as we are here dealing with, 

 statistics indicate a wave-like alteration. Just as in 

 the shape of a wave's front, we see a gentle slope, then a 

 more rapid slope, and then, up to the wave's summit, a 

 gradually diminishing slope, so, in statistical progressions, 

 we recognise a gradual increase at first, then a more rapid 

 increase, then a diminishing increase, until the absolute 

 maximum is reached, after which comes a gradual decrease. 

 But the rear of such a statistical wave may be altogether 

 unlike the front — in other words, the rate and manner and 

 variations of decrease may be quite unlike the rate and 

 manner and variation of increase. It is so with the pro- 

 giess of epidemics, with changes of population in the com- 

 plete history of a nation from its rise to its decadence, 

 with the growth of a trade, with every known subject to 

 which statistical research has been applied. There may be 

 alternate wave like rise and fall, there may be so slow a 

 rate of increase or decrease that the crest or valley of the 

 wave seems long in passing, and the decrease after increase, 

 or vice versd, may so far differ from the preceding phase as 

 to be almost imperceptible ; but in every case there is to be 



recognised, either once or more than once, the wave form 

 of rise or of fall.* 



Now, the consumption of coal is at present, and for very 

 obvious reasons, passing through the more rapidly-ascend- 

 ing portion of its wave of increase. For many years after 

 the first recognition of the value of coal as fuel, the mineral 

 crept slowly into use. With its employment, fresh uses 

 for it were found, the very usefulness of the mineral sug- 

 gesting new wants. Chief among the results which sprang 

 directly from the use of coal as fuel, was the application of 

 the steam-engine to a number of ]jurposes which had before 

 been either unthought of or unattainable for want of proper 

 fuel. The spread of manufacture, of trade, of travel, and 

 general intercommunication, followed in due course, at once 

 directly and indirectly necessitating a continued increase in 

 the quantity of coal employed throughout the Kingdom. 

 These causes are still in full operation ; and it is to be 

 expected that, while this is the case, there will not merely 

 be a steady annual increase in the use of coal (for such an 

 increase would follow from the mere expansion of the uses 

 already discovered for the mineral), but an increase of that 

 increase, on account chiefly of the progress of invention 

 and discovery. 



That this state of things will continue for several years 

 to come may fairly be anticipated ; that for many years to 

 come the average rate of increase in the coal-consumption 

 will be fully equal to that at present observed may also be 

 expected ; but that, before many years are passed, the rate 

 of increase (then higher than now) will be beginning to 

 diminish, thenceforward returning towards its present rate, 

 and passing eventually below its present rate, is to be 

 looked forward to as the natural order of events in the 

 future. Let it be remembered that such a result would by 

 no means imply a falling-ofF in the commercial and manufac- 

 turing acti\-ity of the country. The extension of the em- 

 ployment of coal for known uses has, in several instances, 

 already nearly approached a limit. In other cases, such 

 extension, though still proceeding, is not proceeding 

 at an increasing but at a decreasing rate. This must 

 happen in turn with all the known applications of coal, 

 the extension of its use perhaps attaining a rate cor- 

 responding nearly to that of the actual growth of our 

 population.! Such a change would imply a continual 

 increase of national commercial prosperity, not (as at first 

 view might seem to be the case) a gradual decadence. It 

 is as though a merchant, whose gains, already large, had 

 been increasing year by year, say by £1,000, should find 

 them still increase year after year by £900, £800, £700 

 (the change occupying many years), until, at length, the 



• Let any one try such an experiment as the following, and he 

 will readily understand what is here meant by wave-like progres- 

 sion, and obtain also very convincing evidence of the fact in ques- 

 tion. Along a horizontal line let equal spaces be measured, and let 

 a set of vertical lines be pencilled through the divisions on the 

 horizontal line. Now, from the weekly records of health let the 

 number of deaths due to any disease, or form of disease — as, for 

 instance, diarrhoea, or the class of diseases included under the head 

 zymotic — be noted from the commencement to the end of some 

 period in which such diseases may have been particularly active, 

 and let the nnmber of deaths in successive weeks bo represented on 

 any convenient scale on the successive vertical lines, measuring 

 upwards from the horizontal line. [For example, say that fifty 

 deaths shall be represented by one inch, and other numbers pro- 

 portionately.] Then through the summits of the lines thus drawn 

 let a curve be swept. It will be found that this curve has the 

 wave-figure spoken of above. 



t The population is increasing at an increasing rate at present ; 

 but as this rate is much lower than that at which the consumption 

 of coal is increasing, this consumption, in changing to the rate at 

 which population is increasing, must diminish its rate of increase. 

 Moreover, the increase of the rate at which the population of this 

 country is increasing, grows less, decade by decade. 



