348 



NATURE 



\Aitg. 24, 1876 



ner's method gives,aswe have seen, a line on'which the ship 

 is, and in doing so it gives us all the information which any 

 one sight can yield. But if we possess some other informa- 

 tion, such as a knowledge of the true latitude, the position 

 becomes completely determinate ; each condition gives a 

 locus, and the intersection of the two loci gives a point. 

 By introducing this foreign element into the calculation 

 of the original sight, we may obtain at once the definite 

 information that the ship is in a certain latitude and lon- 

 gitude, and we may do so by a single calculation. This 

 is the practice of ninety-nine navigators out of a hundred, 

 but it is a practice much to be deprecated. It makes the 

 sailor imagine that a knowledge of the latitude, got either 

 by dead reckoning or by taking a meridian altitude, is neces- 

 sary in order that he may get any information at all out of 

 a single observation of altitude and time. If he trusts to 

 obtaining this knowledge by dead reckoning he is likely 

 enough to estimate the latitude wrongly, and by so doing 

 to vitiate the whole calculation. If he trusts to observing 

 the meridian altitude, he is often disappointed by the sun's 

 being clouded over at noon. Many a captain has lost his 

 ship through not knowing how to avail himself (by 

 Sumner's method) of the information which he might have 

 derived from a short glimpse of the sun on a cloudy 

 day. Another danger in the ordinary practice is that it 

 tempts the navigator not to work out each sight as soon 

 as it has been taken, for he must often wait until he is 

 able to obtain the other information, without which he is 

 helpless. But when Sumner's method is used, every sight 

 tells its own tale, and there is no reason whatever why it 

 should not trell it at once. 



The limits of a review do not admit of our describing 

 the manner in which Sir William Thomson has contrived 

 to facilitate Sumner's method. A full explanation of how 

 it has been done will be found in the preface to his book. 

 At first sight it appeared that, in order that tables might be 

 of any use, they would require to contain the solutions of 

 157,464,000,000 spherical triangles, to calculate which, at 

 the rate of 1,000 per day, would take 400,000 years. 

 This did not seem promising, but Sir William Thomson 

 was not dismayed. He soon saw that by dividing the 

 problem into the solution of two right-angled spherical 

 triangles he could give all the required information in a 

 table containing the solutions of only 8,100 triangles. 

 These 8,100 calculations have been made under the super- 

 intendence of Mr. E. Roberts, of the Nautical Almanac 

 Office, and the results are tabulated in the volume before 

 us. Full instructions for their use are appended, along 

 with some auxiliary tables which add greatly to the com- 

 pleteness of the work. Not to go into details, we may 

 say that by an admirable application of the second of the 

 two plans given above for drawing the Sumner line, the 

 author has so shortened the time required to reduce an 

 observation, as to convert what was formerly an objection 

 to Sumner's method into a positive recommendation, and 

 so has deprived sailors of their only possible excuse for 

 not adopting it universally. 



Such a general adoption, besides its direct benefits in 

 increasing the safety of ships and men at sea, could not 

 fail to have a great indirect eff"ect for good in assisting 

 the sailor to a clear perception of the fundamental prin- 

 ciples underlying the processes which he daily employs, 

 too often, we fear, in blind routine. A seaman using 



Sumner's method can hardly help understanding what he 

 is about, but he may work for a lifetime with the hack- 

 neyed formulae in common use, and have no notion from 

 first to last of why he should add a quantity rather than 

 subtract it, or indeed of why he should deal with it at all. 

 We have heard of a captain who used a plus instead of a 

 minus sign for two or three weeks, and first suspected that 

 something must be wrong when he found himself on a 

 coral reef hundreds of miles off his supposed course. 

 When a landsman with a smattering of mathematics goes 

 to sea and is admitted to the privacy of the chart-room, 

 his wonder is, not so much that some ships are lost, as 

 that any ships escape. 



It is not the masters or the mates that are chiefly to blame 

 for this state of things. Before they enter the service their 

 utmost immediate ambition is to get the needed certificate of 

 competency from the Board of Trade, and they naturally 

 study only to pass the required examination. Then after- 

 wards their professional life is not exactly that calm 

 repose which conduces to progress in a scientific know- 

 ledge of their art. There are no doubt exceptional men 

 whose love of their profession is so strong as to override 

 the barriers of circumstance. Such men deserve all 

 praise, but we can hardly blame the rest. For a remedy 

 we must look not to the individual officer but to the 

 authorities who have the making of him. It is strange 

 that the Board of Trade should not have seen it to be a 

 duty to let no British seaman obtain its certificate without 

 showing himself to be thoroughly acquainted with Sumner's 

 method. Until the Board does this it will be mainly, we 

 might say almost wholly, responsible for the prevailing 

 neglect of this method. 



The position of the nautical reformer seems to us to be 

 anything but enviable. His virtue is perhaps its own 

 reward, certainly he seldom meets with any other. The 

 Board of Trade and the Admiralty will have none of him, j 

 and he cannot make much way against the conservatism 

 bred of ignorance that he finds elsewhere. It is still fresh 

 in the memory of every one how Mr, Plimsoll at last com- 

 pelled a reluctant government to take legislative action on 

 behalf of seamen. Unfortunately, Sir William Thomson 

 must confine himself to milder methods : he has no 

 opportunity of shaking his fist in the face of a prime 

 minister. 



OUR BOOK SHELF 



Botanical Tables for the Use of Students. Compiled by 

 Edward B. Aveling, B.Sc. Second Edition. (London : 

 Hamilton, Adams, and Co.). 



Any attempt to compress the facts of nature within the 

 arbitrary limits of a defined tabular statement must ne- 

 cessarily be misleading from a scientific, that is, from a 

 philogenetic, point of view. Classificatory tables have 

 nevertheless their use to the student, in aiding his memory 

 by bringing a large number of facts within a small 

 compass. Dr. Aveling is careful to disavow any inde- 

 pendent value for his tables, and frankly states that they 

 will not only be useless, but positively injurious, if allowed 

 in any way to be a substitute for practical field-work. With 

 these limitations the tables may be recommended as pro- 

 bably as good, or nearly so, as any that could be drawn up. 

 They have been compiled carefully, and on the whole 

 successfully. Defects can no doubt be pointed out. Thus 

 the description of certain inflorescences as " centripetal 

 arranged centrifugally " requires a foot-note to explain its 



