34 



SCIENTIFIC NE\VS. 



[Jan. 13, li 



with a steady flame ; the air supply for the complete 

 combustion being drawn through the openings at F and N. 

 This lamp is eminently portable, is very free from 

 smoke and smell, and ought, at once, to supersede the 

 dangerous benzoline lamps. The manufacturers, Messrs. 

 Nolting, of Mark Lane, do not claim that it is better than 

 the ordinary forms of lamp, but only that it is a safe 

 portable light. From photometric experiments it has 

 iDeen found that these lamps give a light equal to one and 

 three-tenth standard candles, and that the consumption 

 of oil is half an ounce an hour, so that, with oil at eight- 

 pence the gallon, the cost for eight hours is only one 

 farthing. 



— «-^I^><^fe-» — 



A LARGE METEORITE. 



A LARGE mass of meteoric iron has lately been dis- 

 covered in the state of Wisconsin. It was ploughed 

 up three years ago in a cornfield, and attracted atten- 

 tion from its weight and silvery lustre. The farmer 

 supposed it to contain silver, but he was quite ignorant 

 of its true nature. Accordingly it lay about his farm- 

 yard, until lately an acute observer saw what it really 

 was. When it was ploughed up, during the excite- 

 ment about iron ores in the neighbourhood of the 

 field, a speculator chanced to see the large mass 

 and at once paid ^i i for an option on the forty 

 acres to search for iron ore. The mass was sent to 

 Professor Fisher for analysis. On its being discovered 

 to be a meteorite, the owner claimed the curiosity; but 

 the professor was so struck by the size of the mass that 

 he went to the farm to make investigations. He found 

 that it had been struck by the plough near the surface of 

 the ground, in a field that had been cultivated for corn 

 for several successive years ; and the farmer was quite 

 certain that it could not have been there the year before 

 (1883). The fresh, silvery appearance of the mass testi- 

 fied to the probability of its having recently fallen. It is, 

 however, quite remarkable that it kept so bright during the 

 three years it lay in the farmer's yard. No similar pieces 

 have been seen, nor does this show signs of fracture. The 

 mass has been considerably disfigured by attempts to 

 chisel off pieces, and one piece was forged into a spike. 

 When it reached the professor's hands, after the pieces 

 had been chopped off, it weighed 53lbs. It is of irregu- 

 lar shape, 8 by 8 inches across the face, and 7 inches 

 through in the thicker part, but with an average thick- 

 ness of 4 to 5 inches. The reverse side is nearly flat, 

 and pretty uniformly covered with circular juttings. It 

 presents the ordinary appearance of most masses of 

 meteoric iron, the surface crust having entirely dis- 

 appeared. It seems probable that it lay with this sur- 

 face in contact with the ground during the three years 

 after it was dug up, and the crust disappeared by the 

 ordinary process of weathering. The front side is less 

 regular in shape, and shows several large depressions. It 

 is largely covered with the fused crust which is heaped 

 up in ridges, and shows all the peculiarities of the lines of 

 flow characteristic of irons which have been picked up 

 immediately after their fall. The character of this St. 

 Croix meteorite, as it is called, independent of the confir- 

 matory evidence afforded by the circumstance of its 

 history, would make it probable that its fall did not 

 precede by many months the date of its being ploughed 

 up. It contains 90 per cent, of iron, yi of nickel, i| of 

 cobalt, ^ of phosphorus, j of silica, with traces of carbon, 

 copper, and tin. Where did this come from ? 



DUST TRAPS. 



SOME cupboards and drawers seem to have the power 

 of attracting dust. A little consideration will show 

 that there is sufficient reason for expecting that dust will 

 accumulate in such places. Dust is carried about only 

 when the air is in motion, and it begins to settle as soon 

 as the motion ceases. It will naturally settle on any 

 ledges or the edge of cracks. How does it get driven 

 through the cracks or narrow spaces round the doors ? 

 A difference of one inch in the height of the barometer is 

 due to a difference of pressure of about one-thirtieth, and 

 since the volume varies inversely as the pressure, the 

 volume will vary by about one-thirtieth. A cupboard 

 measuring 4 feet by 4 feet by 2 feet, will contain about 

 30 cubic feet of air, allowing for shelves. If it is closed 

 when the barometer is low, and a rise of one inch should 

 take place, in order that equilibrium may be restored, 

 about one cubic foot of air will have to find its way into 

 the cupboard. The pressure with which it will be forced 

 in will at first be about half a pound to the square inch, 

 or 72 pounds to the square foot. A difference of 15 

 degrees of temperature will produce the same result,, 

 and it may happen that the two causes may act at 

 the same time. Unless very considerable care is 

 taken in fitting the doors, it is probable that equili- 

 brium will soon be restored, and any dust that has 

 settled on the ledges will be drawn in ; as soon as it is 

 inside, the air being still, it will settle, and will not be 

 ready to be blown out at the next change. The pressure 

 within the cupboard will be reduced every time the door 

 is opened, the door acting like a piston. This is likely 

 to draw in any dust that is lying near. Cabinets for 

 specimens, etc., should be arranged with flaps or guards 

 to every ledge or crevice, taking care that they do not 

 act as receptacles for dust in themselves. 



The best remedy, however, has been devised by an 

 American curator, who provides each cupboard or 

 drawer with a dust trap. This consists of a large hole at 

 the back, covered both inside and outside with a piece 

 of wire gauze, and the space between, corresponding 

 to the thickness of the board, is rilled with cotton wool. 

 At any change of pressure, due either to natural meteoro- 

 logical causes, or to the opening and shutting of doors,, 

 will produce a displacement of air in this hole. The air 

 meets with scarcely perceptible resistance, all dust 

 lying on the wire gauze is stopped by the cotton, and 

 the result is perfect absence of dust. 



The Largest Brilliant in the World. — Concern- 

 ing the early history of this South African gem very 

 little is known ; in fact, where the stone was found is 

 Duly a matter of conjecture. It is, however, believed that 

 it was found in one of the Kimberley mines. South 

 Africa. It was decided to cut it into the largest ^possible 

 brilliant, still preserving a good shape. The stone in i s 

 finished condition weighs 180 carats, is a beautiful, perfect 

 steel-blue diamond, and is the largest brilliant in the 

 world. It is 39.5 mm. (i 9-16 inches) long, 30 mm. (i 

 11-64 inches) wide, and 23 mm. (15-16 of an inch) thick, 

 being exceeded in size by one diamond only, the Orlofif, 

 belonging to the Russian crown, which weighs 194I 

 carats, but is a large deep rose and not a brilliant. The 

 Victoria exceeds the Regent in weight by 44g carats. The 

 Kohinoor weighs only 106 1-16 carats. The original 

 weight of the stone was 45 7g carats, 3 1-60 ounces troy. 



