73 



in the present paper is to determine this point by the discussion of 

 several years' observations of the tides at Plymouth and at Bristol. 

 The calculations for the former place were executed by Mr. Dessiou 

 and Mr. Ross in the Hydrographer's Office at the Admiralty; the cal- 

 culations for Bristol were performed by Mr. Bunt, in virtue of a 

 grant of money from the British Association. The result of these 

 discussions is, that a very regular form and good approximation for 

 the semimenstrual inequality may be obtained from the observations 

 of one year ; that the existence of the lunar parallax corrections ap- 

 pears very clearly in the observations of one year ; and that its value 

 may be determined from a series of three or four years. The lunar 

 declination corrections are more irregularly given by short series of 

 observations ; but in a series of four or five years, the general form 

 and approximate value of the corrections become manifest. In the 

 course of these calculations such questions as the following v/ere 

 proposed, and their solution attempted : 1 . To which transit of the 

 moon ought we to refer the tide ? It appears that the transit which 

 produces the best accordance with theory, is that which Mr. Lubbock 

 terms transit B, which is an epoch about 42 hours anterior to the 

 high water at Bristol and Plymouth. 2. How does a change of 

 the epoch affect, first, the semimenstrual inequality ; secondly, 

 the parallax correction of the time ; thirdly, the declination correc- 

 tion of the times ; fourthly^ the parallax correction of heights ; and 

 fifthly, the declination correction of the heights? 3. Does the pa- 

 rallax corrections of height vary as the parallax ? 4. Does the pa- 

 rallax correction of time vary as the parallax ? 5. Does the declina- 

 tion correction of the heights vary as the square of the declination } 

 6. Does the declination correction of time vary as the square of the 

 declination } 7. Can the laws of the corrections be deduced from 

 a single year .-^ 8. Are there any regular differences between the 

 corrections of successive years ? 9. Do the corrections at different 

 places agree in themselves ? It does not appear that any change 

 of the epoch will produce an accordance of the observed laws with 

 the theory, some of the inequalities requiring one epoch for this 

 purpose, and some requiring another. The inequalities in different 

 years and different places are also compared. 



Mr. Whewell remarks, that since it has now been shown that 

 good tide tables may be obtained from short series of observations, 

 his researches with regard to the determination of the lunar correc- 

 tions may be concluded ; and the proper mode of farther prosecuting 

 the subject, would be to have tide observations at several stations, 

 each observatory reducing its own observations, and thus constantly 

 improving the tables, as is practised in other branches of Astro- 

 nomy. 



" Researches in Embryology." First Series. By Martin Barry, 

 M.D., F.R.S.E., Fellow of the Royal College of Physicians in Edin- 

 burgh. Communicated by P. M. Roget, M.D., Sec. R.S. 



This paper is divided into two parts. In the first part the author 

 describes the origin and structure of the ovisac, a vesicle common 



