ADVANCEMENT OE SCIENCE. Ill 



we attempt to follow with our eye the motion ofa rotating body, we find it difficult 

 to determine through what point of the body the instantaneous axis passes at any 

 time, — and to determine its path must be still more difficult. I have endeavoured 

 to render visible the path of the instantaneous axis, and to vary the circumstances 

 of motion, by means of a top of the same kind as that used by Mr. Elliott to illus- 

 trate precession. The body of the instrument is a hollow cone of wood, rising 

 from a ring, seven inches in diameter and one inch thick. An iron axis eight in- 

 ches long, screws into the vertex of the cone. The lower extremity has a point of 

 hard steel, which rests in an agate cup, and forms the support of the instrument. 

 An iron nut, three ounces in weight, is made to screw on the axis, and to be fixed 

 at any point ; and in the wooden ring are screwed four bolts, of three ounces, 

 working horizontally, and four bolts, of one ounce, working vertically. On the 

 upper part of the axis is placed a disc of card, on which are drawn four concentric 

 rings. Each ring is divided into four quadrants, which are coloured red, yellow, green 

 and blue. The spaces between the rings are white. When the top is in motion, it is 

 easy to see in which quadrant the instantaneous axis is at any moment, and the 

 distance between it and the axis of the instrument ; and we observe: — 1st. That 

 the instantaneous axis travels in a closed curve, and returns to its original position 

 in the body. 2nd. That by working the vertical bolts, we can make the axis of 

 the instrument the centre of this closed curve. It will then be one of the principal 

 axes of inertia. 3rd, That by working the nut on the axis, we can make the order 

 of colours either red, yellow, green, blue, or the reverse. "When the order of 

 colours is in the some direction as the rotation, it indicates that the axis of the in- 

 strument is that of greatest moment of inertia. 4th. That if we screw the 

 two pairs of opposite horizontal bolts to different distances from the axis, the path 

 of the instantaneous pole will no longer be equi-distant from the axis, but will de- 

 scribe an ellipse, whose longer axis is in the direction of the mean axis of the 

 instrument. 5th. That, if we now make one of the two horizontal axes less and 

 the other greater than the vertical axis, the instantaneous pole will separate from 

 the axis of the instrument, and the axis will incline more and more till the spinning 

 can no longer go on, on account of the obliquity. It is easy to see that, by attend- 

 ing to the laws of motion, we may produce any of the above effects at pleasure, and 

 illustrate many different propositions by means of the same instrument. 



" ON THE BALAKLAVA TEMPEST, AND THE MODE OF INTERPRETING BAROMETRICAL 

 FLUCTUATION," BY MR. T. DOBSON. 



In the month of November, 1854, the passage of a storm over the British 

 islands caused a considerable depression of the barometric column, beginning 

 on the 11th of November and ending on the 19th. During four consecutive 

 days of this period of diminished atmospheric pressure, there occurred in the coal 

 mines of Britain, five fatal explosions, at the following places: — on Nov. 13, at Old 

 Park Colliery, Dudley, Worcestershire ; Nov. 14, Cramlington Colliery, Northumber- 

 land ; Nov. 15, Bennet's Colliery, Bolton, Lancashire, and Birchey Coppice Colliery, 

 Dudley; Nov. 16, Rosehall Colliery, Coatbridge, N. B. These facts alone render 

 this storm worthy of special attention, independently of the notoriety which it has 

 acquired from its disastrous effects on the allied fleets and armies in the Crimea. 

 The meteorological circumstances which characterized the Balaklava tempest have 

 been determined with unusual care and skill, from a very great number of observa- 

 tions at stations spread over the whole surface of Europe, by M. Liais, of the Imperial 



