'52 



HARD WI CKE ' S S CIE NCE - G O SSIP. 



Mr. Galloway has done good service in his perse- 

 vering study of the agency of coal dust in producing 

 colliery explosions. 



He has completely refuted the old-established 

 notion that they are simply due to the combustion of 

 the hydro-carbon gases to which the miner gives the 

 name of " fire-damp." Mr. Galloway has demon- 

 strated clearly that fine coal dust stirred into ordinary 

 air forms a mixture having fearful explosive energy. 

 The only question which he leaves debateable, is 

 whether a destructive colliery explosion may be due 

 to this alone, or whether an initial explosion of fire 

 damp always occurs. 



That such initial explosion, by stirring up the coal 

 dust otherwise lying dormant, and at the same time 

 igniting it, may be in many cases operative is not to 

 be doubted ; but the very practical and very serious 

 question, of whether a pit free from outbursts of 

 carburetted hydrogen may nevertheless be liable to 

 explosions if dry and carelessly worked, still remained 

 open. Mr. Galloway contends that the dust alone 

 is dangerous ; others have denied this, notably so 

 MM. Mallard and Le Chatelier in their report to 

 the French Commission du Grisou. Since this a 

 Prussian Fire Damp Commission has been appointed, 

 and has investigated the subject very thoroughly, their 

 results confirming those of Mr. Galloway. 



The subject is of great and growing importance. 

 "We are rapidly exhausting our old coal seams, and 

 continually going deeper and deeper to supply the 

 voracious demands of our blast furnaces, gas works, 

 wasteful fire-places, &c, and as we get deeper, we 

 come upon dry workings, where, unless special 

 precautions are taken, every shot stirs up a cloud 

 that may contain particles fine enough to produce 

 a local explosion, the which stirs up another cloud to 

 explode in like manner, and so on to fearful results, 

 even in a pit where naked candles may be carried 

 with safety if the air is not violently agitated. The 

 practical bearing of this upon the kind of pre- 

 caution demanded is self-evident. The source of 

 danger being so different from that of fire damp, 

 the precautions must be modified accordingly. 



The commercial results of sewage farming are 

 usually very discouraging. This however has not 

 been the case at Forfar, where, according to the 

 published accounts, a field of 38 acres, which cost 

 ,£3,600, or £94 per acre purchase money, has yielded 

 a profit, the total cost of working being ^220 l$s. 

 including horse labour, manual labour, seed and 

 repairs, and auctioneer's commission. The receipts 

 were ,£509 12s. 6d. leaving a balance of £288 17^. 6d. 

 or 8 per cent, on the capital outlay. This however does 

 not include any management expenses, but supposing 

 a capitalist to have undertaken it, and managed his 

 own business and thereby saved the £24 5^. 2d. charged 

 for auctioneer's commission, he would have obtained a 

 return of nearly 9 per cent, with very little trouble. 

 We appear to be within measurable distance of 



returning to the soil nearly all we take from it, 

 thereby restoring our rivers to their pristine purity 

 and vastly increasing our food supplies. If the still 

 continuous downfall of rentals urges the landlords to 

 give to this subject the degree of practical attention 

 which their own interests demand, we may have 

 reason to exclaim with the banished duke, that "sweet 

 are the uses of adversity-" 



TEETH OF FLIES. 



By W. H. Harris. 



No. VI. 



(STOMOXYS CALCITRANS.) 



THE genus from which the present illustration is 

 taken, forms a small one of the order Diptera, 

 embracing, according to Walker, three species only, 

 viz., Stomoxys calcitrans, S. irritans, and S. stimulans. 

 Towards the close of summer, and during the autumn, 



''"'<?-) V 7 ' 



Fig. 98. — Mouth of Stomoxys calcitrans X 14 diam. ph, ph, 

 pharynx ; Ibr, labrum ; /, lingua ; la, labium ; mp, maxillary 

 palpi ; le, levers or fulcra of labrum. 



S. calcitrans enters our houses, and, by its persistent 

 and aggravating attacks on mankind, does much to 

 destroy the equilibrium of the best of tempers. It is 

 commonly known as the stable fly, but is not at all 

 disinclined to pay attention to oxen, &c. So similar 

 is it in general outward appearance to the ordinary 

 house-fly, that, unless special attention is directed to 

 the mouth organs, it may easily be mistaken for 

 Musca domestica, but while the latter is compara- 

 tively an inoffensive creature, the former is an 

 unmitigated nuisance ; in fact, the only redeeming 

 point about it is of a purely negative character. 

 Possibly by stimulating the attacked party to take 

 some exercise to rid the pest, it may do some good, 

 but the benefit thus derived is more than counter- 

 balanced, if a quiet after-dinner nap has been 

 contemplated. The proboscis is cylindrical, with an 

 enlargement near its point of attachment to the head. 

 Unlike the Muscidse, it is incapable of being with- 

 drawn, but always projects from the head downward 

 and slightly forward. It is chitinous, black, hard, and 

 beautifully polished. Under the microscope, about 

 three-fourths of the circumference is seen to be 

 thickly set with very delicate transverse striae, and 



