SOME NOTES ON JUPITER DlTRINa HIS OPPOSITION OF 1876. 97 



DISCUSSION. 



Me. H. C. Eussell said, that Mr. Hirst had done a valuable 

 work in watching so closely the changes which had taken place 

 in the planet Jupiter during the present winter. A great many 

 curious things had appeared. 



Mr. Hirst had tried to collect the observations made upon the 

 white spots, and to show that they had some connexion with the 

 periods of the maximum sun-spots. If such a connexion could 

 be shown satisfactorily, it would have much interest ; but in 1863 

 he (Mr. Hussell) saw the white spots on Jupiter most distinctly. 

 He had never seen them so well since, and 1860 was the maximum 

 sun-spot period before 1870. 



The black spots were similar in form to the white spots. A 

 theory had been hazarded that perhaps they were cyclones opening 

 up the cloud envelope which is supposed to reflect the sun's light 

 to us. If so, the persistence they maintain in their relative 

 distances is very curious. He (Mr. Eussell) had not been able 

 to delect any difference in their position for a considerable time. 

 Jupiter is 1,300 or 1,400 times the size of the earth, yet his revo- 

 lution only takes 10 hours. If these cloud accumulations are 

 produced by the revolution of the planet, the velocity of the 

 currents must, therefore, be something enormous. Some of the 

 markings on the planet Jupiter have been seen to recur years 

 after, and we cannot conceive of any peculiar cloud-form recurring 

 after a number of years. It seems probable that something solid 

 has been seen on these occasions. We cannot expect cloud-forms 

 to have that definite character and to retain it. His own opinion 

 was that the great changes which had occurred within short 

 intervals were simply changes in the state of definition, not 

 changes on the planet, but changes in our power to see it. He 

 had lost sight of certain features one night, and seen them 

 another night. 



In June, when we had a great change in the state of our 

 atmosphere, the colour of the planet was altered. He thought 

 the colour of the planet depended on the state of the air over 

 our heads. The colours of the stars depend on something very 

 mysterious. Being struck with the differences of colour observed 

 through different telescopes, he had put a graduated scale of 

 colours, varying from green to red, through yellow and orange. 

 Through the telescope there came to view a definite point at which 

 the yellow changed to pink — a point not visible to the naked eye 

 at all. With a silver-glass reflecting telescope he observed the 

 same phenomenon. He could only explain this by supposing that 

 the pink had been put over the yellow. 



