33-4 Intelligence and Miscellaneous Articles, 



Occult ations of Stars. § 14. Observations of Eclipses from 1620 

 to 172-1. § 15. Discussion of Deviations in the Moon's mean Mo- 

 tion. § 16. Motion of the Moon's node. § 17. Concluding Remarks 

 on the Value of the Secular Acceleration deduced in this paper. 



For the subjects treated in the sections above enumerated we 

 must refer the reader to the work itself, in which will be found 

 evidence of the skill with which the author has accomplished his 

 task, and the results at which he has arrived. In section 15, de- 

 voted to the discussion of Deviations, the author, speaking of the 

 cause of outstanding deviations, remarks that we may make two 

 hypotheses : — (1) That these deviations are only apparent ones, 

 arising from inequalities in the axial rotation of the earth. The 

 deviation of the observed secular acceleration from the theoretical 

 value 6"*18 has long been attributed to a retardation of the earth's 

 rotation ; and by supposing this retardation to be a variable quan- 

 tity, and indeed sometimes to change into an acceleration, we may 

 completely account for the observed deviations. (2) We may sup- 

 pose the deviations to arise from one or more inequalities of long 

 period in the actual mean motion of the moon. On the first of 

 these hypotheses the author says, " If it is correct, the problem of 

 predicting the moon's motion with accuracy through long intervals 

 of time must be regarded as hopeless, since it cannot be expected 

 that variations in the earth's axial rotation will conform to any de- 

 terminable law. Success in tracing the deviations in question to 

 the moon itself, and to the theory of gravitation, is therefore a 

 consummation to be hoped for." 



In the last section, containing the concluding remarks on the 

 value of the secular acceleration deduced by the author, he suggests 

 that " either the recently accepted value of the acceleration and the 

 usual interpretation of the ancient solar eclipses are to be radically 

 altered, the eclipse of —55Q not having been total at Larissa, and 

 that of —514 not having been total in Asia Minor, or the mean 

 motion of the moon is, in the course of centuries, subjected to 

 changes so wide that it is not possible to assign a definite value to 

 the secular acceleration. 



An important feature of this book consists of the collection of 

 observations of eclipses and occultations (some hitherto unpub- 

 lished) used by the author in his investigation. Altogether the 

 work forms a valuable addition to the literature of the Lunar 

 Theory. 



XXXIX. Intelligence and Miscellaneous Articles. 



ON A VISUAL PHENOMENON AND ITS EXPLANATION. 



BY WILLIAM ACKB.OYD, F.I.C. 



TTISTJAL phenomena are of general interest, and are often de- 



* scribed but seldom explained. The phenomenon in question 



may be seen under the following circumstances. Face the breeze, 



and without winking allow a small raindrop to fall on the surface 



