Mar. 2, i8S8.] 



SCIENTIFIC NE^A^S. 



197 



and in the reverse direction in the southern hemisphere. 

 Such a whirlwind is called a cyclone. It is not neces- 

 sarily a storm. Its diameter may be from one to 

 two thousand miles, but in imagining it as an inverted 

 whirlpool we must remember that it is only about ten 

 miles deep. In the northern hemisphere cyclones move 

 in a general east-north-easterly direction, at a rate of 

 from 100 to 1,000 miles a daj^ 



The barometer is lowest at the centre, and rises 

 gradually as the outside of the cyclone is approached. It 

 must not be imagined that such a depression of the 

 barometer indicates a corresponding depression of the 

 atmospheric ocean above us, for there is reason to believe 

 that in high levels the depression disappears, and it is 

 not improbable that at a height of 15,000 feet or so the 

 pressure is greater over the centre of a cj'clone than at 

 its extremity. 



We may find an analogy in the currents ol a swiftly- 

 flowing river. The friction of the bottom retarding the 

 water, the velocity near the surface is greater than near 



surface. There is no evidence to show there are 

 currents in the upper regions of the atmosphere of 

 sufficient strength to give rise to cyclones in this manner, 

 but the analogy may assist the reader to imagine the 

 circulation of the currents. 



When the air from the upper regions descends a rise 

 of pressure is noticed, and there is a circular motion, not 

 so strong as in a cyclone, but very clearly defined. It is 

 less easy to imagine why there should be a circular 

 motion in this case, especially when we find that the 

 direction is always opposite to that of a cyclone, viz., 

 in the direction of the hands of a watch. Such an 

 area of high pressure is called an anti-cyclone. The 

 direction of the currents of air at the surface of the 

 earth is represented in fig. i, an anti-cyclone being 

 shown on the left and a cyclone on the right. There is 

 a large area of calm in the centre of an anti-cyclone. 

 fig. 2 is a diagram of the state of the barometer, and is 

 supposed to represent the same district as fig. i. A line 

 is supposed to be drawn through all places where the 

 barometer is at the same height. 



(To be continued^ 



NEW SAFETY LAMP. 



MESSRS. HINKS AND SONS have patented a new 

 safety burner for oil lamps, of which we give an 

 illustration. The burner is provided with an ex- 

 tinguisher, which acts automatically the moment the 

 lamp is a little out of the perpendicular, so that if 

 the lamp is knocked over by accident the flame is ex- 

 tinguished before the oil reservoir has had time to come 



the bottom. This would tend to make the upper part 

 run away from the lower ; but the deficiency is met by 

 an occasional uprush of water from the bottom, and it is 

 generally carried a little above the surface by its 

 momentum, forming a swelling from which the water 

 spreads radially. The uprush is evidently due to a 

 reduction of pressure, which sucks the water upward, 

 and the swelling above the surface of the stream is of 

 course attended by a slight rise of pressure near the 



H inks' Safety Lamp. 



in contact with the ground. The way in which this is 

 done is exceedingly simple. The lever shown to the 

 left of the illustration is attached to a spiral spring, and 

 the instant the little catch, shown to the right of it, is 

 released the spring causes the extinguisher to fly up and 

 put out the flame. The heavy ball to the right is suspended 

 from a ball and socket joint, which permits it to move 

 freely in all directions. When moved out of the perpen- 

 dicular it pushes up the collar attached to the catch and 

 thus releases the extinguisher lever. We tried the 

 effect of slowly inclining the lamp so as to cause the ball 

 to act very slowly, but in no case did we succeed in 

 tipping the lamp more than 45 degrees before the ex- 

 tinguishing action came into play. The invention is 

 ingenious, and the mechanism is not liable to get out of 

 order. 



