1869.] Astronomy. 97 



disc, but is apparently pear-shaped. This phenomenon is due to 

 the effects of irradiation, by which the sun's apparent diameter is 

 increased, while that of the planet is diminished. But the great 

 dilficulty in judging of the observations made in 1769 has lain in the 

 necessity of following some law or other as to the choice of what 

 shall be held to be the true moment of internal contact. The error 

 which Stone has discovered in Professor Encke's mode of treatment 

 consists in the fact that the latter did not apply a uniform law to 

 the observations which came under his notice ; that, in fact, in one 

 or two instances, he misinterpreted the words of the observers. " I 

 consider," says Mr. Stone, " that by simply interpreting strictly the 

 language em])loyed by the observers, I have been led to a solution 

 which satisfies the whole of the ten observations, and gives, at the 

 same time, from the equations of condition, a satisfactory result for 

 the difference between the time of internal contact and the breaking 

 of the black drop." The value of the solar parallax deduced from the 

 new treatment of the observations is 8" 91, a value which agrees 

 in the most satisfactory manner with that which had been obtained 

 as the mean of other methods of estimating the parallax. 



We must remark, however, that Professor Newcombe considers 

 Mr. Stone's interpretation of the observations made in 1769 as un- 

 tenable. 



Mr. J. Tebbutt, jun., suppHes a series of observations made by 

 him upon the star ij Ai-giis. He compared this singular variable 

 with neighbouring stars. It appears from these observations, that 

 f} Argus has not exceeded the sixth magnitude during the past two 

 years. Thus we are compelled to reject the theory of Professor 

 Wolf, who assigned a law of variation according to which the epoch 

 of minimum briUiancy should have occurred in 1861, and the mag- 

 nitude of the star should have been 3*6. Certainly 75 Argus is the 

 most remarkable star in the whole heavens. A quarter of a century 

 ago, it outshone the brilliant Canopus, and rivalled Sirius itself in 

 splendour ; now it can only just be detected with the naked eye on 

 a very clear night. 



Two biennial meetings have been held of the Astronomische 

 Gesellschaft, under the presidency of Professor Argelander, and the 

 heads of the subjects discussed appear among the notices of the 

 Astronomical Society. Amongst these, we may notice the follow- 

 ing: — It has been suggested that the older observations of the 

 Periodic Comets should be re-examined. Four points have been 

 specified — the new determination of the places of the stars of com- 

 parison, the calculation of the auxiliary quantities with the now- 

 received values of the constants for the times of the appearance of 

 the comets, the calculation of solar ephemerides for these times, 

 and lastly, the pubhcation of the originals of the older comet 

 observations. It appears that the calculations for the comets of 



VOL. VI. H 



