Sept. 21, 1882] 



NATURE 



501 



In every respect the most interesting and valuable part 

 of the work are the concluding chapters of vol. ii., in 

 which all the fresh geographical materials are conveniently 

 summed up, the land revenue system of Persia dealt with 

 probably for the first time in a really satisfactory manner, 

 and the present condition of the country made the subject 

 of some opportune remarks. It is pleasant to learn that 

 this venerable monarchy, so far from being " played 

 out," is even beginning to show signs of renewed vitality. 

 The famine-stricken districts are gradually recovering, 

 the peculiar underground system of irrigation is being 

 largely extended, brigandage has been almost everywhere 

 suppressed, the governors are beginning to show some 

 regard for the interests of the people, while many will 

 perhaps be surprised to hear that the people themselves 

 are, on the whole, more comfortable, better clad, and 

 better fed than the Indian rayats. There is, of course, 

 " much to be done in the way of governing and reducing 

 things to order ;" but notwithstanding much maladminis- 

 tration and many local grievances, '' the progress made 

 by Persia within the last ten years is unmistakable." 



The work is supplied with a series of excellent sectional 

 maps of the regions traversed by the explorer. But there 

 is neither index nor a table of contents beyond the 

 briefest chapter-headings. The stages, however, along 

 the routes are in all cases carefully recorded, with their 

 distances and time occupied in covering the ground. 



A. H. Keane 



Notes on Chemical Calculations, with Examples, for use 

 in /lie Leys School. By A. Vinter, M.A. (Catley; 

 J. S. Newsome, 1882.) 



The selection of calculations contained in this little book, 

 while exhibiting nothing new, is satisfactory ; the notes, 

 in so far as they are explanatory of the calculations, are 

 clear, and to the point, but when they deal with such 

 subjects as atoms, molecular weights, and equivalency, 

 they become sadly confused ; on these points they must, 

 we are afraid, be very misleading to the boys who make 

 use of this book in the Leys school. 



A Pocket Guide to British Ferns. By Marian S. Ridley. 



(London : Bogue, 1881.) 

 Miss Ridley's book merits its title ; for it is of a most 

 convenient size for the pocket. Whether a nesv book on 

 British ferns was needed may fairly be doubted ; but this 

 little volume will be useful to many beginners. The cha- 

 racters of each fern are given in tabular form, each occu- 

 pying a page ; and the principal points of distinction are 

 clearly brought out. 



LETTERS TO THE EDITOR 

 [The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 

 [ The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible otherwise to ensure the appearance even 

 op communications containing interesting and novel facts.] 

 A Meteorological Spectroscope 

 As a considerable amount of interest seems to have been 

 awakened lately in meteorological spectroscopy, it maybe of 

 ! ervice to observers to call their attention to a form of pocket 

 spectroscope specially adapted for this purpose « hich Mr. Adam 

 Ililger, of 192, Tottenham Court Koad, prepared for :.:e some 

 months ago. The compound triple prism of flint glass is 

 counted as nearly as possible at the minimum angle of devi ition 

 for " C." We thus obtain a much better view of the red end 

 of the spectrum thai with the ordinary pocket spectroscope. 

 Mr. Hilger has also managed to secure an increa ed dispersion 

 which, with very perfect definition, enables me to see the lines 

 in the so-called ' ' rain-band " at " D " w ith great ease. 



Besides the ordinary achromatic object-glass between the 



adjustible slit and the prisms, the spectroscope is fitted with a 

 telescope, i.e. a sliding tube carrying a lens, or second object- 

 glass, in front of the slit— proposed by Mr. Lockyer— to bring 

 the light from external objects to a focus on it. By this means 

 one is able to differentiate, or localise, the spectra of different 

 parts of the sky. I feel sure that the use of the telescope would 

 prevent people falling into some of the mistakes one sees in 

 publications about rain- band spectroscopy. 

 September 14 1. f. D. Donnelly 



The New Comet 



On Sunday morning, the 17th inst., at 10.45 a.m., I found a 

 bright comet near the sun. The nucleus was bright, stellar in 

 appearance ; the tail was about 4' long, and brightest at the outside 

 edges, giving a double appearance. The direction of the comet 

 was to the centre of the sun. The comet preceded the sun's 

 centre at 10.59 by 6m. 50s., at 12K 0111. by 5m. 44s. The dis- 

 tance from the sun's limb on the parallel was at nh. 10m, 18' 

 8" (of arc), and at I2h. 6:n., 13' 4". 



I hoped to get more an I Letter measure-, but the sky overcast, 

 and with the exception of a short Itime on Monday morning' 

 when I looked but did not see, the comet has remained so. 



I used a helioscope of six inches' aperture. 



Ealing, September 19 A. A. Common 



Contact Makers of Delicate Action 

 I have allowed an error to creep into the sectional elevation 

 of the contact-maker described in your last issue. The bent 

 wire merely dips into the capsule at D, and is separate from the 

 w ire, which passes up the tube. This latter wire merely forms 

 part of the circuit, being connected with the terminal as shown 

 in the plan. It should be noted that the plug K is only inserted 

 when the contact-maker is being moved about. Except when 

 this is the case, the mercury passes freely through the opening at 

 M, and nothing but the fiction of mercury resists the motion of 

 the wire. 



Some remarks made in the discussion on the paper have led 

 me to carefully examine the end of the platinum wire dip- 

 ping into the mercury at D. It is shown (highly magnified) in 

 the annexed figure. This end being softened, and no doubt 



End of Platinum \V 



brought to a welding state by the heat, of which the spnrk is the 

 visible evidence, has, in rapidly beating upon the mercury, been 

 apparently hammered into this shape. 'I he nodules upon it are 

 probably those referred to in books on chemistry as one to the 

 expulsion of occluded hydrogen. The result shown in the figure, 

 produced with a strong current (15 Groves cells) and a small 

 wire, could in practice be easily prevented. 



H. S. Hele Shaw 

 University College, Bristol, September 15 



Bobbers 

 In his well-known account of the habits of the Pearly Nautilus, 

 Rumphius (D'Amboinsche Rariteitkamer, door G. E. Rum- 



