284 



KNOWLEDGE ♦ 



[Xov. 9, 1883. 



them — " Loss of life ! " exclaims Mr. Ruskin, cheerfully. 

 " By the ship overwhelmed in the river, shattered on the 

 sea; by the mine's blast, the earthquake's burial — you mourn 

 for the multitude slain. You cheer the lifeboat's crew ; 

 you hear with praise and joy the rescue of one still breath- 

 ing body more at the pit's mouth ; and all the while, for 

 one soul that is saved from the momentary passing away 

 (according to your creed to be with its God), the lost souls 

 yet locked in their polluted flesh, haunt, with worse than 

 ghosts, the shadows of your churches and the comers of 

 your streets ; and your weary children watch, with no 

 memory of Jerusalem, and no hope of return from their 

 captivity, the weltering to the sea of your Waters of 

 Babylon." Oh .' Goroo ! Goiioo-oo ! 



Any philosophy which hopes for other than misery and 

 disgust in life, must indeed seem strange doctrine to 

 teachers such as these, — even as the smiles of the cheerful 

 seem unmeaning and oflensive to those whose souls are 

 overcast with gloom and discontent. Sir Walter Scott tells 

 a story of his childhood which well illustrates the un- 

 reasoning hatred felt by the Everlasting Growl school for 

 the doctrine that conduct should be directed to the increase 

 of happiness. One day, his healthy young appetite made 

 him enjoy very heartily the brose or porridge of the family 

 breakfast. Unluckily ho was tempted to say aloud how 

 good he found his food. His father at once ordered a pint 

 of cold water to be thrown in, to spoil the taste of it ! Pos- 

 sibly he meant to inculcate what he regarded as a high 

 moral habit ; but rather more probably Mr. Walter Scott, 

 sen., objected to his son's enjoying what he had no taste 

 for himself. Much of the sourness of the Growl Philosophy 

 may be thus interpreted. 



[To he continued.) 



THE SUN'S DISTANCE.* 



By Professor Pi. S. Ball, LL.D., 



ASTKONOMEE-KOYAL FOR IRELAND. 



(Continued fi'om page 257.) 



1"^HE most celebrated method of measuring the distance 

 from the earth to the sun is without doubt that 

 which is afTorded by the transit of Venus. This has en- 

 grossed more than all the other methods together. On 

 four occasions the attempt has been made to find the sun's 

 distance by its aid ; the last of these occurred only last 

 December, and another opportunity will not occur until 

 June in 2,004. It was formerly supposed, and it is, no 

 doubt, still maintained by many, that the transit of Venus 

 is par excellence the method, but the growth of practical 

 astronomy has tended to question the supremacy of the 

 transit of Venus. An attack has been made in two dis- 

 tinct directions. It has on the one hand been shown that 

 the transit of Venus is incapable of the accuracy that was 

 at one time claimed for it. On the other hand the new 

 method by the aid of the minor planets has arisen. 



The recent transit of Venus was observed in this country. 

 It was on December 6 last, late in the afternoon, that the 

 memorable event took place. The weather, it may be re- 

 membered, was in most places very unfavourable. A 

 heavy snowstorm prevailed over a great part of the 

 coimtry. At Dunsink Observatory, Dublin, where I 

 reside, a more unfavourable morning could not well have 

 lieen conceived. The snow was falling, the clouds were 

 thick, and there did not seem to be the slightest chance 



* A discourse delivered at the second general meeting of the 

 British Association at Southport. 



that anything could be seen. The day before was tolerably 

 fine, and we had a sort of rehearsal of the observations to 

 be made. The large equatorial was directed to the sun, 

 and it was followed to the horizon. As the sunset ap- 

 proached the sun passed behind a tree and could not be 

 seen. This was one use of the rehearsal ; it showed that 

 the tree was an obstacle. I pointed this out to the kind 

 neighbour in whose grounds the tree was placed, and next 

 morning the top was cut ofl'. 



On the eventful day, and up to about half-an-hour before 

 the commencement, there did not seem to be a chance that 

 any observations would be obtained, but we placed every- 

 thing in readiness as if the day had been perfect. Just 

 before the critical mo)nent the snow ceased, the clouds 

 began to break, and though the commencement was missed, 

 I enjoyed a beautiful glimpse of the planet when its disc 

 had about half entered on the face of the sun. It was, 

 however, but little more than a glimpse, for the clouds 

 again gathered and the snow descended, giving me for a 

 few moments an exquisitely beautiful telescopic jiicture of 

 a snowstorm, with the sun's disc as a background. For an 

 hour nothing could be seen. Then again the clouds opened 

 and disclosed what I can only describe as a most beautiful 

 and striking picture. The sun had commenced to put on 

 the ruddy hues of sunset. Its disc was streaked with 

 bands of clouds, and far in on the surface hung the dark 

 body of the planet. It was one of those rare sights which 

 once seen can never be forgotten. 



Good fortune has generally attended the expeditions 

 which last December were scattered far and wide over the 

 earth to observe the transit of Venus. A map is prepared 

 to indicate the various regions in which the diflerent 

 phases of the transit were visible. The British Isles are 

 seen just to fall into the region in which the commence- 

 ment of the transit is visible. In the eastern parts of 

 Europe and the whole of Asia the entire is invisible. The 

 western hemisphere contains more favoured regions. The 

 most glorious views of the transit of Venus were those 

 obtained in America. In the centre of the region where 

 the whole transit is visible lies the splendid empire of 

 Brazil. The only part of the American continent which 

 was unfavourably situated was the British possessions at 

 the North. 



We cannot now enter into details as to the method by 

 which the transit of Venus is used for the purpose of 

 finding the sun's distance. Every book on astronomy 

 contains a description of the process. It will be my 

 duty to attempt to define the amount of accuracy of which 

 the method is capable. The observations to be employed 

 are chiefly those made when the planet and the sun are 

 apparently in contact, and the value of the method 

 mainly depends on the possibility of determining the time 

 with precision at which the contact takes place. 



It was at one time believed that exceptional accuracy 

 was attainable in such observations. Experience has not 

 shown that these expectations were well founded. Look, 

 for example, at a photograph of the drawings made on the 

 last occasion by one of the most skilfid observers. Dr. 

 Vogel. We have here six most beautiful views of the pro- 

 gress of Venus as it approached to the first internal con- 

 tact. The two extreme observations are plain enou h. At 

 3 h. 10-8 rain. Venus had not entered on the ^^ce of 

 the sun completely. At 3 h. 14-1 min. there can oe no 

 doubt that the critical moment had passed. Th -e are 

 four intermediate stages. The recorded time of coiitact is. 

 3h. 13 min. 1.5 sec, but there must be a latitude of many 

 seconds in the attempt to define a moment so confused. 



The chief reason of the difficulty arises from the sluggish 

 motion of Venu-s. The problem is something like trying 



