Oct. 19 1876] 



NATURE 



559 



mind of the student as possible ; and this, we think, might 

 best be accomplished by prefixing to each chapter diagram- 

 matic sections of the succession of strata, exhibiting their 

 equivalences in different parts of the country. Again, 

 although we recognise with the author the impossibility 

 of quoting in such a work as the present the authority for 

 every statement, yet we think that a well selected series 

 of references to those original memoirs, in which fuller 

 details concerning each formation may be found, would 

 greatly add to the value of the book without materially 

 increasing its bulk. 



We cannot but commend the manner in which Mr. 

 Woodward has resisted all attempts at fine writing, and has 

 sought rather to produce a work characterised by accu- 

 racy and soundness than by showiness and superficiality ; 

 in this respect following the example of his father, the 

 late Dr. Samuel Woodward, to whose memory the work 

 is dedicated. We anticipate for the " Geology of.England 

 and Wales " a sphere of usefulness not less extended than, 

 and a reputation as enduring as that which has been 

 attained by, the " Manual of the MoUusca ; " and higher 

 praise it would scarcely be possible to award to it. 



It only remains to add that the work is illustrated, not 

 only with a very clear chromo-lithographed map prepared 

 by Mr. Griesbach, but by woodcuts of such excellence (as 

 will be manifest from the specimens we give of them) that 

 we can only regret that they are so few in number. 



J. W. J. 



SUMNER'S "METHOD AT SEA" 



T N reference to our review of Sir William Thomson's 

 ■^ work on this subject (vol. xiv. p. 346), our attention 

 has been called by Sir G. B. Airy to the following paper 

 in the Proceedings of the Royal Society, vol. xix. p. 448 : — 



" Remarks on the Determination of a Ship's Place at Sea." In 

 a Letter to Prof. Stokes. By G. B. Airy, LL.D., &c., 

 Astronomer-Royal. 



Royal Observatory, Greenwich, S.E., 

 1871, April 5. 



My dear Sir, — In the last published number of the Proceed- 

 ings of the Royal Society (vol. xix. p. 259), there are remarks by 

 Sir William Thomson on the proposed method for determining 

 the locus of a ship's place at sea, by making one observation of the 

 sun's (or other body's) altitude, and founding, on this, computa- 

 tions of longitude with two assumptions of latitude ; and there 

 are suggestions, with a specimen of tables, for solving the 

 spherical triangles which occur in all similar nautical observations, 

 on the principle of drawing a perpendicular arc of great circle 

 from one angle of a spherical triangle upon the opposite side. 



In regard to this principle and the tables which may be used 

 with it, I may call attention to the employment of a similar 

 method by Major-General Shortrede, in his " Latitude and 

 Declination Tables," pp. 148 and 180. In p. 150, line 11 from 

 the bottom, it will be seen that the "column " gives the trial- 

 value of the perpendicular arc by which the two right-angled 

 triangles are computed. This is not the same (among the various 

 elements which may be chosen) as Sir William Thomson's ; but 

 it is so closely related that in some instances the tabular numbers 

 are identically the same as Sir W. Thomson's, though in a dif- 

 ferent order. General Shortrede's object was "Great Circle 

 Sailing," in which the trigonometrical problem is the same as in 

 the nautical observation. I think, however, that Sir W.Thomson 

 deserves thanks for calling attention to the application of this 

 method to time-determinations. 



In regard to the problem of the "locus," allow me to point 

 out the geometrical circumstances of the case. If, upon a celestial 

 globe, an arc of small circle be swept with the sun's (or other 

 body's) place for centre, and the observed zenith-distance for 

 radius, the ship's zenith will be somewhere in that curve ; and 

 if, with the pole for centre, arcs of parallels be swept with the 

 two assumed colatitudes for radii, the intersection of these two 

 curves with the first drawn curve will give the ship's zenith on 

 the two assumptions ; and if within the celestial globe there be 

 placed a small terrestrial globe, and if these zenith-points be 

 radially projected upon the terrestrial globe, the terrestrial places 



of the ship on the two assumptions will be marked. But the 

 practical application of this requires that the position of the ter- 

 restrial globe, or of the earth, be known in respect of rotation — 

 that is, it requires that the Greenwich sidereal time, or solar 

 time, be known ; in other words, it requires a perfect chrono- 

 meter. Now the experience of Capt Moriarty, cited by Sir W. 

 Thomson, does not apply here. Capt. Moriarty received time- 

 signals from the Royal Observatory through the cable every day, 

 and he had therefore a perfect chronometer. But other ships 

 have no such perfect chronometer ; and though the direction of a 

 locus, as determined above, may be sufficiently certain, yet its 

 place upon the earth will be uncertain, by a quantity depending 

 on the uncertainty of the chronometer. Thus three chronometers 

 may give the following positions for the locus-curve : — 



Chron. No. i. Chron. No. 2. Chron. No. 3. 



And the question now presents itself, which uncertainty is the 

 greater — the uncertainty of latitude, which it is the real object 

 of this problem to remedy ? or the uncertainty of the chrono- 

 metric longitude, which must be used in attempting to find the 

 remedy ? I do not doubt the instant reply of any practical 

 navigator, that the chronometric longitude is far more uncertain 

 than the latitude ; and if it be so, the whole method falls to the 

 ground. 



I fear that a publication like that which has been given to this 

 method may do very great injury among navigators who are not 

 accustomed to investigate the geoiretrical bearings of such 

 operations, and may lead them into serious danger. 



I am, my dear Sir, yours very truly, 



G. B. Airy. 



Prof. Stokes, Secretary of the Royal Society. 



[From a general recollection of a conversation I had with Sir 

 W. Thomson before the presentation of his paper, I do not 

 imagine his object to have been exactly what the Astronomer- 

 Royal here describes, but partly the saving of trouble in nume- 

 rical calculation, partly the exhibition, for each separate obser- 

 vation of altitude at a noted chronometer time, of frecisely what 

 thai observation gives, neither more nor less, which introduces at 

 the same time certain facilities for the determination of a ship's 

 place by a combination of two observations. Of course the 

 place so determined is liable to an error east cr west correspond- 

 ing to the unknow n enor of the chronometer ; and doubtless, 

 under ordinary circumstances, this forms the principal error to 

 which the determination of a ship's place is hable. This remains 

 precisely as it did before ; and it is hard to suppose that the 

 mere substitution of a graphical for a purely numerical process 

 could lead a navigator to forget that he is dependent upon his 

 chronometer, though perhaps the general tone of Sir W. Thom- 

 son's paper might render an explicit warning desirable, such as 

 that which Mr. Airy supplies.— G. G. Stokes.] 



NOTES 



We hear with sincere regret of the death of the eminent 

 French meteorologist, M. Charles Sainte-Claire Deville. We 

 hope next w eek to give some details of his life and work. 



We publish on another page an abstract of the Rev. Mark 

 Pattison's forcible and outspoken address at the Social Science 

 Congress, Liverpool, on the state of our universities. Many other 

 valuable papers were read, but they were for the most part too 

 special for notice in our columns. We should, however, mention 

 the remarks of Mr. W. H. James, M.P., in connection with the 

 discussion of the question of incorporating a professional and tech- 

 nical training with a sound system of general education. Mr. 

 James traced the history of the City Guilds of London, showed 

 how enormously wealthy they must be, how this wealth is 

 totally misspent, and maintained that the country had a perfect 

 right to ask an account of their stewardship, and appropriate the 

 funds, if necessary, for educational purposes. He proposed that 



