160 



ARCTIC AND ANTARCTIC CURRENTS. 



[1855. 



sented the mass suspended in a stout ring, ^hidh was furnished 

 with jji-ojeeting axles, like the ring of the gymbal. These axles 

 could be jjlaced in a small frame of wood, bushed with brass. 

 This small frame, when placed on a piece of smooth board, could 

 be turned freely round by turning the piece of board on which 

 it rested as long as the gyroscope was not revolving, friction 

 being sufficient to cause the one to turn with the other ; but 

 when the gyroscope was set rapidly revolving, in vain you at- 

 tempted to turn the frame, by turning the board on which it 

 rested, so determinately did it endeavour to mairtain its own 

 plane of rotation, as quite to overpower the friction. In the 

 third modification of the gyroscope, it was suspended in gymbals, 

 so exquisitely constructed that both the gyroscope proper and 

 the supporting gymbals were accurately balanced, so as to rest 

 freely when placed in any position in relation to the earth. By 

 this the author showed most strikingly the effect of any attempt 

 to communicate revolving motion round any other axis to a 

 mass already revolving, for, on placing the gymbals in a frame 

 of wood while the gyroscope was not revolving, it remained 

 quite steady ; but, when thrown into rapid revolving motion, 

 the slightest attempt to turn the frame round to the right or to 

 the left was instantly followed by the entire gyroscope turning 

 round in the gymbals, so as to bring its axis to coincide with 

 the new axis you endeavoured to give it, with a life-like preci- 

 sion,, and always so as to make its own direction of revolution 

 be the same as that of the slightest turn you impart to it. 

 Having thus demonstrated the necessary effect of combining one 

 rotatory motion with another, he then proceeded to demon- 

 strate palpably that the earth's revolving motion affected the 

 gyroscope in precisely a similar way. Having, by the screw 

 adjustments, brought the gyroscope, in gymbals, to a very exact 

 balance, it remained fixed in any position when not revolving. 

 But rapid rotatory motion having been communicated to the 

 gyroscope mass as soon as the gymbal supports are placed on 

 the stand, you see the entire apparatus, slowly at first, but 

 at length more rapidly, turn itself round, nor ever settle until 

 the axis, on which the gyroscope is revolving, arranges itself 

 parallel to the terrestrial axis, in such a sense as to make the 

 direction of the revolving gyroscope be the same as that of the 

 whole earth. He next showed that the determination with 

 which it did this was sufficient to control the entire weight of 

 the instrument, though that amounted to several pounds, for, 

 taking the ring gyroscope, from the side of the ring of which a 

 small steel wire projected, ending in a hook, the wire coinciding 

 with the prolongation of the axis of the gyi-oscope ; of course, 

 when not made to revolve, the hook, if placed in a little agate 

 cup at the top of a stand, would permit the instrument by its 

 weight, to fall instantly, as soon as the support of the hand was 

 taken from it. But, upon imparting to it rapid rotatory motion, 

 it stood up even beyond the horizontal position, so as to bring 

 its axis of rotation nearly to the same inclination to the horizon 

 as the axis of the earth, while the whole acquired a slow 

 rotatory motion round the point of the hook ; and so steady 

 was its equilibrium wliile moving thus, that a string being- 

 passed under the hook and both ends brought together in the 

 hand, the whole may be lifted by the cord off the stand and 

 carried revolving steadily about the room. Next, to show the 

 motion of the earth sensibly, he placed the gymbal gyroscope 

 suspended freely by a fine silk fibre in a stand with the lower 

 steel point of its support resting in an agate cup; along light 

 pointer projecting from the ring carried a pointed card which 

 passed over a graduated card arch of a circle placed concentri- 

 cally with the gyroscope ; upon imparting rapid rotatory motion 

 to the gyroscope the index was seen as the earth moved to 



point out the relative motion of the plane of rotatum exactly in 

 ^he same way : the law of the motion being also the same as that 

 of the well-known pendulum experiment. Lastly, he set the 

 ring gyroscope in motion, and by placing a small pointed piece 

 of brass at the end of the axle on the ring, the instrument 

 went immediately through all the evolutions of a boy's top 

 on the floor, humming meanwhile loudly also. 



On Arctic and Antarctic Currents, and their Connexion with 

 the Fate of Sir John Franklin. 



Jii/ Mr. a, G. Findlat. * 

 Allusion was made to a former paper, read to the Association 

 at Hull last year, describing the euiTcnts of the Atlantic and 

 Pacific Oceans, in the latter of which it was thought some new 

 features were described. It was shown that a great similarity 

 existed in the movements of the two oceans, — a system of 

 westerly drifts between the tropics, which on arriving at the 

 western side of each ocean turned north and south from the 

 ecjuator on each side of it, and re-curving when beyond lat. 30° 

 N. and S., they passed to eastward, and re-entering their course 

 on the eastern sides, they formed a complete circulatoiy system. 

 In the present paper it was shown how the Polar regions were 

 connected with these movements, and how tropical warmth 

 reached the poles, and the cooling effects of the extreme 

 climates were brought into more temperate zones. The nature 

 of the enormous magnitude of the antarctic ices, which offer a 

 perfect contrast to those of the North Pole, was explained. — 

 From the southern part of the southern connecting current, 

 which encircles the southern part of the globe between lat. 40° 

 and 50° S., a system of S.E. drifts is found, impelled by the 

 prevailing N.W. winds. These drifts, as found by Capts. Sir 

 J. Ross, DuiTille, Wilkes, Ballery, and others, run at a rate 

 between ten and twenty-five miles per day towards the vast icy 

 barrier whose limits, as far as known was explained. This enor- 

 mous collection around the South Pole is purely the result of 

 atmospheric deposition, and is remarkable as lying to the south 

 of the greatest area of ocean water on the earth's surface, 

 and over which the winds pass towards it ; but from the fact 

 of all countries in south latitude having arid climates, and 

 those in the north the reverse, this was another evidence that 

 the evaporation of the northern hemisphere is deposited in 

 the south, and in'ce versa. One fact analogous to those 

 observed in the North Atlantic Ocean, — of dust once supposed 

 to be volcanic, but proved to be microscopic Crustacea, — was 

 cited as occurring near to the antarctic circle, and also adding 

 a confirmation of the theoiy of the atmospheric circulation. 

 The face of the icy barrier, consisting of cHffs elevated from 

 150 to 210 feet above the sea level, perfectly wall-faced, and 

 extending continuously for hundreds of miles, was an evidence 

 that ocean currents did not penetrate that circle, which we only 

 know from its external edge. These table-topped barriers were 

 the result of surface deposition, and, being above 1,000 feet 

 thick, were of sufficient solidity to be protruded bodily down- 

 wards from the interior lands, which might consist of moun- 

 tains of solid ice of sufficient inclination seawards to allow the 

 set of the stratified upper portions to glide downwards, bearing 

 on their under surfaces immense quantities of earth and de- 

 tached rocks. The floating ice met with in such large quan- 

 tities is the result of the breaking up of the detached table- 

 topped crags, and from the face of the cliffs, and not on the 



* Athenseum. 



