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
