552 FOURTH REPORT — 1834. 



tarded, and thus interfere with each other ; a theory which has 

 been suggested by other authors. 



It is acknowledged that the above hypotheses are arbitrary. 

 The object is to show that there is no incongruity between the 

 undulatory theory and the phaenomena of absorption. For it 

 may be observed, the above hypotheses do not at all interfere 

 with the laws hitherto assumed in the calculations of the undu- 

 latory theory. When the laws of the absorption here spoken 

 of are known, the undulatory theorist will have before him the 

 task of pointing out what is the constitution of transparent me- 

 dia. The object of the present remarks is to show that the 

 existence of a constitution which shall embrace the facts as far 

 as we know them, is not at all at variance with the undulatory 

 theory. 



On the Visibility of the Moon in Total Eclipses. By the 

 Rev. T. R. Robinson, D.D., 8^c. 



Some years since, the late Sir John Leslie brought forward 

 an hypothesis, that the planets, and in particular the moon, 

 shine, not, as is commonly supposed, by reflected light, but by 

 a kind of phosphorescence ; either absorbing solar hght and 

 emitting it with some modification, or becoming luminous in 

 consequence of its action. He supported this opinion with his 

 visual ingenuity, and in particular availed himself of the argu- 

 ments afforded by the moon's secondary light, and the red ap- 

 pearance of her disc in total eclipses. The first of these he 

 thought far too intense to be the result of " earthshine," and 

 the second still more disproportioned to that which is com- 

 monly reputed its cause, the refraction of rays transmitted 

 through the earth's atmosphere. His reasoning on these facts 

 is, however, vitiated by defective data, for he cei'tainly under- 

 rates the reflective force of unpolished surfaces, and exagge- 

 rates the moon's light ; and the author would not have reverted 

 to it but for an appearance that presented itself during the 

 eclipse of December 26th, 1833. While the moon was enter- 

 ing the shadow, the eclipsed portion exhibited the usual yel- 

 lowish red glare, which in this case, from the great illuminating 

 power of the telescope, was very striking, giving the idea of an 

 immense globe of brass faintly ignited. This was least bright 

 but most coloured at the eastern limb, and the division between 

 it and the portion still enlightened by the sun was made by a 

 zone of blueish grey light about 30" or 40" broad, which was 

 seen by several persons with this telescope. This disappeared 

 when the moon was totally immersed. At the middle of the 



