MERCURY VENUS THE EARTH. 



it, without attempting to take measurements, till it became impossible to do so, owing to 

 the clouds returning. Both observers received the sun's image through a telescope in a 

 dark room upon a piece of white paper. 



The transits of Venus are of special interest from their rarity and great physical 

 importance. They occur at intervals of eight years, a small section of individual life ; but 

 alternating with intervals of more than a century, during which whole generations pass 

 away, thrones crumble, and dynasties change. They are of importance as the very best 

 means of ascertaining the distance and volume of the sun, which supply data for 

 determining the distances and magnitudes of the planets, and serve as a universal standard 

 of astronomical measurement. The second recorded transit, in 1761, was well seen; but 

 the discordance of the results obtained at different stations shook faith in the accuracy of 

 the observations. For the third and last, in 1769, many of the European governments 

 sent costly expeditions to various parts of the globe ; and among others, Captain Cook was 

 despatched to witness the phenomenon at Tahiti. The next transit will occur December 9, 

 1874; and though not visible in this country, it will be watched elsewhere with an 

 intensity of scientific solicitude which no natural incident has ever yet excited, and with 

 much better instruments than have before been used. Another will follow after an interval 

 of eight years, December 6, 1882, which will be seen in England, 

 but only partially, commencing near sunset. Venus will not 

 again be seen upon the sun's disk through the whole of the next 

 century, or till June the 8th, 200-i. 



But little is known of the physical constitution of Venus, owing 

 to the intense splendour with which she shines. The existence of 

 a considerable atmosphere is inferred from the appearance of a 

 penuinbral light round the planet during her transits, as well as 

 from a faint radiance observed to stretch beyond her directly 

 illuminated hemisphere. The line in the annexed uppermost 

 figure marks the boundary of the direct influence of the sun's 

 rays ; and the upper and lower projections beyond it show the 

 twilight, which is referred to atmospheric reflection. Variable 

 and fleeting spots have also been repeatedly noticed, as in the 

 second figure, which naturally leads to the supposition of an 

 atmosphere charged with clouds and vapours, with water upon 

 the surface, from which they are formed. The conclusion that 

 she has mountains and valleys rests upon the fact that the edge 

 of her enlightened part appears shaded, that her corners are 

 sometimes obtuse, and present a luminous point apparently de 

 tached from the planet. Schroeter regarded this as the summit 

 of a high mountain, illuminated by the sun after he had ceased 

 to be visible to the rest of that hemisphere. If these conclu 

 sions may be depended upon, and they are warranted by strong 

 evidence, Venus presents striking points of analogy to the con 

 stitution of the earth. An atmosphere reflecting light, the 

 medium of sound, and a highway for " fire and hail, snow and 

 vapour," a superficies exhibiting the diversities of land and 

 water, hill and vale these are some of her probable attributes, 

 features expressing a family likeness to our globe, and indicating 

 the action upon her surface of that mighty upheaving agency, 

 which, in bygone ages, piled the Alps, and reared the ramparts 

 of the Himalaya. 



