154 ANNUAL OF SCIENTIFIC DISCOVERY. 



and deposited on board a vessel by the 31st May next, in order that it may be 

 laid down during the succeeding months of June and July. The English 

 Government has acted with the utmost liberality. It has directed a vessel to be 

 sent out at its own expense, to make further and thorough soundings, and to 

 examine the coasts of Ireland and Newfoundland, with a view to select the 

 best places for landing the cable. It has also agreed to guarantee an interest 

 of four per cent, per annum on the entire amount of capital required to manu- 

 facture and lay down the cable. 



It is proposed to construct the cable of seven copper wires, covered with three 

 separate layers of gutta-percha, over which is to be bound hemp saturated 

 with tar and other materials, the whole being inclosed in 126 iron wires. 



ON THE EXTERNAL TEMPERATURE OF THE EARTH AND OTHER 

 PLANETS OF THE SOLAR SYSTEM. 



"We obtain the following paper by Mr. Hopkins, on the above subject, from 

 the Proceedings of the Cambridge (England) Philosophical Society: 



"We have not sufficient data to determine the superficial temperature of 

 any planet except our own. "We know, however, that it must mainly 

 depend on the temperature of the planetary space, and on the heat which 

 the nearer planets at least receive directly from the sun, but modified, and 

 possibly in a far greater degree than has been generally supposed, by the 

 particular circumstances by which each planet may be characterized. No 

 astronomer, judging from the appearances which Mars and Jupiter present to 

 us, would entertain any serious doubt as to the existence of atmospheres 

 surrounding those planets, and the probability would seem to be almost 

 equally strong of Saturn being likewise enveloped in a similar manner. The 

 obliquity of the axis of rotation is known with considerable accuracy in the 

 case of Mars and Jupiter, and also in that of Saturn, if it coincide with the 

 axis of rotation of his ring. Venus presents great difficulties to the observer, 

 but it appears now pretty satisfactorily determined that the period of rotation 

 about her own axis is nearly the same as that of the earth, and that the 

 obliquity of her axis is large, amounting to as much as about 75. This 

 must produce an extraordinary difference between the changes of annual 

 temperature in that planet and those which we experience. The author has 

 endeavored, in this paper, to estimate numerically the effect of this anomalous 

 obliquity. Practical astronomers have entertained the opinion that Yenus 

 likewise has an atmosphere. Of Mercury we know too little by direct obser- 

 vation to form any opinion on those points founded on observed facts, and 

 the same remark will apply to the remoter planets beyond Saturn ; but most 

 astronomers probably feel much the same conviction that Mercury, Uranus, 

 and Neptune, have atmospheres of greater or less extent, as that they revolve 

 round their own axes with greater or less angular velocity. The earth's 

 atmosphere is known to be almost completely diatherrnanous for heat radiat- 

 ing directly from the sun ; and it is assumed to be equally so for the heat 

 which proceeds directly from the fixed stars, and to which the general tem- 

 perature of space is due. 



