342 



NA TURE 



{Aitgztst 8, 1889 



containing potassium chlorate for which safety is claimed. 

 It is really quite incomprehensible how people w'th the 

 slightest knowledge of chemistry can propose mixtures 

 containing potassium chlorate and organic substances, 

 and in many cases even sulphur as well. 



By drawing the attention of chemists to the amount 

 of nonsense palmed off on the Patent Office, this little 

 book will se ve a good turn ; but it is also of practical 

 value, as extracts from the specifications are given in 

 many cases which may save much seeking. 



Some advice at the end of the book is useful, especially 

 to those interested in explosives in a professional way, but 

 who are not sufficiently chemists to be able to deduce it 

 for themselves. Possibly it is the fault of the speci- 

 fications, and not the author, that benzene is written in 

 several ways, benzole, benzine, &c. 



On p. 68 there is an equation to represent the products 

 of gun-cotton when detonated, to which perhaps some 

 exception may be taken, but after all but slightly, for 

 there is still much ignorance on the matter. It is 



2CoH,0,3\03 = 9CO + 3CO2 + 7H,0 + Ne. 

 It is very doubtful indeed whether any of these nitrates 

 can be burnt under any conditions without yielding a 

 considerablequantity of oxides of nitrogen as end products; 

 probably NO in the first instance, which takes up oxygen 

 fiom the air, and is undoubtedly the greatest drawback 

 in the use of gun-cotton, glycerol nitrate, and similar 

 substances. 



Some advice is given about nitro-glycerine on p. 39. 

 " Any indication of acid fumes or tinge of green should be 

 followed by their prompt destruction with suitable pre- 

 cautions." It would have been well here to give some 

 precautions even at the risk of repetition, for it is not safe 

 to play with nitro-glycerine when in this state. The 

 author might have added that an addition of aniline at 

 this stage renders the destructive operations much safer. 



Under the heading of smokeless and " noiseless " gun- 

 powder, little more could be said at the present time than 

 the author has ventured upon. We do not quite believe 

 that a " noiseless" explosive will be so easily found as a 

 smokeless one. Such a substance belongs almost to the 

 category of explosives that act in " one direction only," or 

 have no recoil. 



We think the book will be useful in several wAys. 

 Blank pages are inserted for further additions to our stock 

 of explosives, safe and unsafe, as they are published. 



W. R. H. 



Gaseous Fuel. By B. H. Thwaite. (London : Whittaker 

 and Co., 1889) 



This little book of forty-six pages contains the substance 

 of a popular lecture delivered by the author, under the 

 auspices of the Manchester and Salford Noxious Vapours 

 Abatement Association. It gives an account of the prin- 

 ciples which underlie the economical consumption of fuel 

 in general, and of the various forms of " gaseous fuel " 

 in particular, and more especially of those forms in which 

 the lecturer is professionally interested. The book, of 

 course, makes no pretensions to deal with the subject 

 exhaustively : its main object, apparently, is to direct 

 attention to the advantages of smokeless fuel as com- 

 |)ared with coal as ordinarily burnt. The author is oc- 

 casionally to be found tripping in his chemistry and 

 physics, and there are, now and then, a few awkward 

 turns of expression. Thus, we read that fire-damp " is a 

 light carburetted hydrogen, one of the gaseous paraffines 

 or methane, its principal formula being chiefly CH4"! 

 (p. 15). The inventor of the well-known laboratory 

 l)urner is styled "Baron Bunsen." On p. 34 we read: 

 '' The principle of the development of motive power by 

 the instantaneous combustion of gaseous fuel rests in the 

 laws of Charles Gay Lussac and Boyle— £'r^<:?, that the 

 pressure exerted by a gas varies directly as its volume." 



The author seems to imply that the idea of using the 

 fire-damp at Hebburn Colliery, near Newcastle, originated 

 in a suggestion made by him some two years ago in 

 Engineer itig. In reality, the idea is due to the younger 

 Buddie. Indeed, as a matter of fact, blowers which have 

 been encountered in the process of working have been 

 frequently utilized either for heating or illuminating pur- 

 poses ; notable examples are at Llwynypia and at Pandy, 

 in the Rhondda Valley. 



A Treatise on Spherical Trigonometry , and its Applica- 

 tion to Geodesy and Astronomy. With Numerous 

 Examples. By Dr. J. Casey, F.R.S. (London : 

 Longmans, 1889.) 



This is a sequel to the large " Plane Trigonometry " by 

 the same writer, and is naturally drawn up on the same 

 plan. Its size is handy, and yet it contains a very large 

 amount of matter. Much of this the author claims to be 

 original, and a great deal, as in the case of the " Plane 

 Trigonometry," has been collected from the foreign 

 mathematical journals. The first three chapters cover 

 familiar ground, with here and there a new feature in- 

 serted. Chapter i v., entitled " Various Applications," gives 

 properties of transversals, of isotomic and isogonal 

 conjugates, of the Lemoine and symmedian points, and 

 of some other lines with which recent plane geometry 

 has made us familiar — more especia'ly our author's own 

 " Sequel to Euclid." Chapter v. discusses the spherical 

 excess, and in chapter vi. we have a full account of small 

 circles on the sphere. The subject of inversions is dis- 

 cussed in chapter vii., and in chapter viii. we have full 

 details of the poiyhedra. The last chapter gives an 

 account of numerous applications of the subject, as to 

 geodesy and astronomy. It would be almost impossible,. 

 we should say, to light upon a theorem elsewhere which 

 is not contained here. More than 500 exercises afford 

 scope for practice. As in the case of the " Plane Trigo- 

 nometry," the author's great indebtedness to Prof. Neuberg, 

 of Liege, is suitably acknowledged, for it is through this 

 gentleman's courtesy the book is brought so thoroughly 

 into touch with Continental sources of information. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents . Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other pai-t of NATURE. 

 No notice is taken of anonyitious communications. ] 



Coronae round a Light produced by a Peculiar 

 St ucture in the Eye. 



For some years past I have been aware that a bright light on 

 a dark background appeared to be surrounded by faint coloured 

 rings, and that these rings were due to something in the eye 

 irseif. But I gave them little attention, for I imagined they 

 were formed in the same way as the coronse seen when the sun 

 or moon is covered by a thin cloud ; opaque particles in the 

 cornea, or little elevations or depres-^ions of its surface, playing 

 ihe part of the drops of water in the cloud. This is the view 

 taken in Verdet's great work on the wave-theory of light. 

 " Les cercles irises, qu'a la suite de cerfaines infi 'mmations de 

 la conjonctive on aper^oit autour des corps lumineux, se rat- 

 tachent a la meme cause que les couronnes ; ces ap[>arences sent 

 dues a i'existence de granulations Ire -petiies et sensiblement 

 e|;ales dans la portion de la conjonctive qui se trouve en avant 

 de la cornee transparente " (Verdet, " Le9 'HS d'Optique 

 Physique," § 79). I have lately discovered, however, that the 

 phenomenon in my own case must be due to quite a different 

 cause. 



A leadint; characteristic of the diffraction phenomena produced 

 by a number of equal obstacles, irregidnrly spaced, is the bright 

 disk surrounding the light, which is for the most part nearly 

 white. Near the light it is bluish, while the outer border passes 

 through yellow to red. To the red succeeds purple, blue, green, 



