Mr. Lubbock on the Tides in the Port of London. 127 



parallax might influence the result ; its effect is difficult to de- 

 termine exactly, but it must be nearly insensible. 



As this coincidence has been misunderstood, I may remark 

 that the calculated times were made to correspond with the 

 mean of the observed times in two places only ; namely, in those 

 which correspond to the moon's southing at two and five hours: 

 their near agreement throughout, proves that the form of the 

 expression from which the calculated times were deduced, 

 is correct. Their coincidence in the first of these points 

 amounts to inferring from the observations the values of the 

 constants A and a': their coincidence in the second amounts to 



inferring the value of the fraction 



m P3 



to' P3 



from the observa- 



tions, the difference would be altogether inconsiderable if the 

 received values of the quantities m, m', P, and P', had been 

 adopted. This mean result is not affected by the neglect of 

 the equation of time which is perhaps perceptible in the table 

 of page G6, in the Companion to the British Almanac. 



The observations seem to inchcate a mass of the moon greater 

 than tliat which has been deduced from the j)hoenomena of 

 precession and nutation; but to determine so delicate a point, 

 the observations must be discussed and examined with greater 

 care, and the effect of the inequality oi variation 'u\\\\Q moon's 

 paralhix considered. 



I regret that I was misinformed with respect to the manner 

 in which the lime was obtained. It was not taken from Ro- 



therliithe 



