Oct. 1st, 1887.] 



SCIENTIFIC NE\VS. 



175 



can skulls two thousand years of age exhibit the same 

 conditions, yet there is no race of men edentulous. " Are 

 the teeth of the present century worse than those of the 

 last ? " is a quesion by no means easily answered, for we 

 have only general observations and no statistics to go by. 

 Dental surgery is a modern art, and too much separated 

 from its parents — medicine and surgery — to satisfactorily 

 decide the question. Moreover, dentists only see those 

 people who have defective teeth. Again, much more im- 

 portance is attached to teeth than in former days, and they 

 consequently receive more attention. It has often been 

 pointed out that the vast improvements in medical and 

 surgical treatment serve to keep alive a large number of 

 weaklings who would otherwise have died, and these often 

 have a progeny of similar frailty, whose teeth we may 

 legitimately conclude partake of the general infirmity. On 

 the other .hand, dental disease, if early treated, as is 

 now done, may be to a great extent stamped out. Of 

 course, the teeth of civilised nations are worse than those 

 of savages, although, as has been remarked in our columns, 

 those cf the latter are by no means free from disease. — 

 Lancet. 



Lightning Conductors. — Professor Tyndall lately ad- 

 dressed the following letter to the Times .-—Some years ago 

 a rock lighthouse on the coast of Ireland was struck and 

 damaged by lightning. An engineer was sent down to 

 report on the occurrence, and as I then held the honourable 

 and responsible post of scientific adviser to the Trinity 

 House and Board of Trade, the report was submitted to me. 

 The lightning conductor had been carried down the light- 

 house tower, its lower extremity being carefully embedded 

 in a stone, perforated to receive it. If the object had been 

 to invite the lightning to strike the tower, a better arrange- 

 ment could hardly have been adopted. I gave directions to 

 have the conductor immediately prolonged, and to have 

 added to it a large terminal plate of copper, which was 

 to be completely submerged in the sea. 1 he obvious con- 

 venience of a chain as a prolongation cf the conductor 

 caused the authorities in Ireland to propose it, but I was 

 obliged to veto the adoption of the chain. The contact of 

 link with link is never peifect. I had, moreover, beside 

 me a portion of a chain cable through which a lightning 

 discharge had passed, the electricity in passing from link to 

 link encountering a resistance sufficient to enable it to 

 partially fuse the chain. The abolition of resistance is abso- 

 lutely necessary in connecting a lightning conductor with 

 the earth, and this is done by closely embedding in the earth 

 a plate of good conducting material and of large area. The 

 largeness of area makes atonement for the imperfect con- 

 ductivity of earth. The plate, in fact, constitutes a wide door 

 through which the electricity passes freely into the earth, its 

 disruptive and damaging elTects being thereby avoided. 

 These truths are elementary, but they are often neglected. 

 I watched with interest some time ago the operation of 

 setting up a lightning conductor on the house of a neigh- 

 bour of mine in the country. The wire rope, which formed 

 part of the conductor, was carried down the wall, and 

 comfortably laid in the earth below, without any terminal 

 plate whatever. I expostulated with the man who did the 

 work, but he obviously thought he knew more about the 

 matter than I did. I am credibly informed that this is a 

 common way of dealing with lightning conductors by 

 ignorant practitioners, and the Bishop of Winchester's 

 palace at Farnham has been mentioned to me as an edifice 

 " protected " in this fashion. If my informant be correct, 

 the " protection " is a mockery, a delusion, and a snare. 



Fire-Proof Fabrics. — The Lancet remarks that it has 

 long been known that all fabrics, even the most delicate 



gauzes and muslins, may be rendered uninOammable by 

 chemical treatment. Of course they cannot be made incom- 

 bustible, but they can easily be so prepared as to be incapable 

 of bursting into flame. The chemical agents employed act 

 by checking and modifying the destructive distillation which 

 precedes what is properly known as inflammation. The 

 chemicals most commonly used for the purpose are alum, 

 borax, phosphate of soda, sal-ammoniac, and tungstate of 

 soda. Alum acts injuriously on the fabrics, especially if 

 coloured, but the others are commonly harmless, and most 

 of them are cheap. Tungstate of soda is the best. Used 

 singly it is apt to become insoluble and to rub off, but this 

 risk can be diminished by the addition of about 3 per cent, 

 of phosphate of soda. After the ordinary washing, the 

 goods should be immersed before wringing and drying in a 

 solution containing 20 per cent, of tungstate with a propor- 

 tionate quantity of phosphate. 



THE DUST IN THE AIR. 



W'E might suppose that with no dust in the air we should 

 at least have more light ; but while it is undoubtedly 

 true that the sunbeams show us the motes, it is no less true 

 also that the motes and fine dust actually show us the sun- 

 beams, and that one is invisible without the other. A beam 

 of sunlight or electric light, if admitted into a chamber in 

 which the air is perfectly pure, at once disappears, and is 

 replaced by pitchy blackness, except where it strikes the 

 wall or some other object. Balloonists tell us that the 

 higher they ascend the deeper becomes the colour of the 

 sky, until at the height of a few miles it looks almost like a 

 black canopy, because, though the sun is shining in un- 

 clouded splendour, there is little or no dust to scatter his 

 light. The space between the stars — inter-stellar space, as 

 it is called — is, accordingly, absolutely black, notwithstand- 

 ing the blaze of light which passes through it and becomes 

 visible on striking our dusty atmosphere. 



The dust in the air we breathe is kept out of our lungs, 

 where it would be injurious, by the innumerable fine hairs 

 or cilia which cover the air passages, and filter the air ; but 

 when the strain is too great and prolonged, the hairs cease 

 to act, the membrane of the air passages becomes inflamed, 

 and bronchitis or asthma follows. The dust of coal mines 

 and that caused by grinding, especially steel-grinding, and 

 the polishing of pearl buttons, marble, etc., particularly 

 where emery is used; also the dust in potteries and china 

 works; the organic dust and fluff of shoddy and flax mills, 

 as well as that arising from the sorting of type, are all in- 

 jurious, and some of them fatal, in their effects upon the air 

 passages and lungs, which the hairs are quite unable to 

 protect. A seedsman once complained to Professor Tyndall 

 that his men were made quite ill during the busy season by 

 the irritation produced by the dust from the seeds, and gladly 

 accepted his suggestion that they should be provided with 

 respirators made ( f cotton wool tied up in muslin, which 

 filtered the air so perfectly that no further complaints were 

 heard. The " black lungs " of colliers are well known, and 

 stony dust is found deposited in the lungs of some masons ; 

 but under ordinary circumstances, except in large towns, the 

 natural filtering apparatus is quite effectual, the particles 

 being arrested by the hairs above-mentioned and then sent 

 back into the air by the expired breath. The air which we 

 breathe out at the end of an expiration is so absolutely free 

 from dust that if we breathe across the track of an electric 

 beam the latter will be pierced by an intensely black hole, 

 for the reasons already given. — New South Wales Indepen- 

 dent. 



