January 31, 19Q1] 



NATURE 



325 



in Oceania and elsewhere would follow the good 

 example of this indefatigable and public-spirited German 

 trader. 



The Story of Thought, and Feeling. By F. Ryland. 



Pp. 219. (London : George Newnes, Ltd., 1900.) 



Price \s. 

 Psychology is not for those who require !=poon-feeding. 

 Many, however, nowadays need a rallying-point for 

 allusions in current literature to a fashionable science, 

 and some would fain still perturbations aroused by the 

 self-consciousness of their children's teachers. To such 

 Mr. Ryland offers a little book which is clear and con- 

 crete, and as condensed as possible without loss of these 

 qualities. He confines himself to an interesting account 

 of certain mental phenomena, aims rather at description 

 than explanation which can be controverted, and his 

 book is excellent of its kind. Mr. Ryland is familiar 

 with the most modern authorities, and presents a fasci- 

 nating subject-matter attractively. Mental imagery is 

 most successfully treated. Mr. Ryland employs the 

 selectiveness of attention inadmissibly as an argument 

 against any form of materialistic theory (p. 22), and he 

 is too vague on the relation of will, self, and kindred 

 formulas ; but his story is so far a story that it in general 

 steers clear of controversies the solution of which lies 

 beyond its scope. It can be confidently recommended 

 to the public for which it caters. H. W. B. 



A Primer of Astronomy. By Sir Robert Ball, LL.D., 

 F.R.S. Pp. viii-M83. (Cambridge University Press, 

 1900.) Price i.f. bd. net. 

 While in many respects this little book seems likely to 

 provide a useful introduction to the study of astronomy, 

 it is to be regretted that greater assistance is not given 

 to those desirous of observing the heavens for them- 

 selves. Even without the aid of a telescope the beginner 

 may easily make observations, more particularly of ap- 

 parent motions, which will go far to encourage a real 

 interest in the subject. 



A wide range of subjects is touched upon, and most of 

 the explanations are clear and concise. Many of the 

 descriptive parts are also excellent. Some of the more 

 elementary phenomena, however, as the phases of the 

 moon, receive very scant treatment, and the principal 

 astronomical instruments are neither illustrated nor ade- 

 quately described. Eleven beautiful plates, mostly from 

 well-known photographs, form the most notable feature 

 of the book. 



Hand in Hand ivith Dame Nature. By W. V. Burgess. 



Pp. x -i- 240. (Manchester : Sherratt and Hughes, 



1900.) 

 Rural life and scenes contemplated in an expansive 

 frame of mind provide excuses for the publication of 

 many pretty books. This one does not differ essentially 

 from many others fashioned on the same model. A 

 country scene, a general knowledge of natural history, 

 an impressionable nature, and a certain facility in the 

 expression of poetic sentiment, seem the chief qualifica- 

 tions of the contributors to literature of this kind. .\ 

 preface is followed by a " prelude," a dog is " a canine 

 friend," and its runs are " peregrinations." We also read 

 of " larks singing in the meridian blue," the brook " which 

 whilom rippled its pure waters over a bed of cleanest 

 sand," "the realm of spiritual immutabilities," "the 

 obyte of summer," and other fanciful matters. The book 

 is not without some attractive and instructive notes on 

 animate nature, but they are almost lost in a maze of 

 platitudes and inconsequent remarks. The statement 

 on p. 39 that grains of corn "have been found in 

 Egyptian mummy-cases, from which marvellously prolific 

 stems have been raised in this country " contains a 

 popular belief as to the growth of mummy-wheat which 

 has been shown over and over again to have no scientific 

 foundation. 



NO. 1631, VOL. 63] 



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 7vriters of rejected 

 mdnuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.^ 



Eclipse Photography. 



In a previous letter (vol. Ixii. p. 246) the writer called attention- 

 to the possible advantage of positive or reversed photography and 

 development in the light in its application to eclipse work. Since 

 that time veiy considerable improvement has been made in the 

 methods, and it is now easy to develop, in direct sunlight, plates 

 which have been somewhat over exposed. The pictures obtained 

 in this way are as clear and sharp as any that can be obtained 

 in the dark room by ordinary methods. But I have not been 

 able to secure details on such plates that cannot be secured on 3. 

 negative by ordinary means. In addition, the over-exposure 

 needed in order to obtain a fine picture is not yet small enough 

 to warrant the usefulness of reverse photography in eclipses. 



In the measurement of the actinic values which are required to 

 yield various results on the photographic plate, a discovery has 

 been made which will be of value in the development of eclipse 

 photographs. It has been found that a plate which has been 

 over-exposed as much as two thousand times can be developed 

 as a clear, sharp negative in the dark room. This can be done 

 by the addition of four or five drops of saturated hypo solution 

 to a two-ounce bath of hydrochinone developer. A half ounce 

 of Cramer's mixed hydrochinone bath with an ounce and a half 

 of water and five drops of the hypo solution in place of the 

 potassium bromide, gives clear and brilliant negatives, but they 

 are slow in developing. They can probably be developed more 

 quickly by making the bath more strongly alkaline. With a 

 normal exposure, the addition of two drops of hypo enormously 

 retards the development. The plate may look perfectly clean 

 for half an hour or more, but the picture will surely appear by 

 giving it time and keeping the bath in absolute darkness. It 

 may require an hour and a half or more to secure complete 

 development. With experience, which may easily be obtained 

 in the use of the hypo-developer, there is no need that any valu- 

 able photographic plate should ever be lost by over-exposure if a 

 proper exposure has been attempted. If the plate cannot be re- 

 placed, and loss from over-exposure is possible, a trace of hypo 

 should always be used at the start in the developer. 



With the hypo developer it is possible to develop on a 

 Cramer "Crown" plate, either in the dark room or in the light 

 room, any exposure not in excess of one million candle-meier- 

 seconds. The highest limit of exposure for the development of 

 good negatives in the dark room is one which permits the de- 

 velopment of positives in the light. A plate two thousand 

 times over-exposed may be developed either as a positive or as 

 a negative. Francis E. Nipher. 



St. Louis, Mo., January 12. 



P.S. — This communication has been made somewhat prema- 

 turely, in order to direct the attention of those who will take part 

 in the work of the next eclipse to a matter which may have great 

 importance. It may be that the over-exposures with which I 

 have been dealing are less than has been stated. It is, perhaps, 

 open to question whether a fast plate under a thin positive, and 

 exposed in a printing frame for three-and-a-half minutes at one 

 meter from a three-hundred-candle incandescent lamp, is two 

 thousand times over-exposed. There is, however, no difficulty 

 in developing such a plate as a negative. 



The Jamaican Species of Peripatus. 



Peripaliis jamaicensis, Grabh. and Ckll., was described in 

 Nature, vol. xlvi. p. 514. At that time it was supposed that 

 all the Jamaican specimens represented a single variable species, 

 but the differences observed were considerable, so that the writer 

 [Zool. Anz., xvi. 341) later separated two " mutations," named 

 gosset and swainsonae. M. E. L. Bouvier has of late years been 

 making admirable studies of Peripatus and its allies, and having 

 procured from London and Cambridge the original Jamaican 

 specimens, he finds that there are in reality two species repre- 

 sented (^.yi?«;-«. Micr. Science, xliii. 755). These he classifies 

 as follows : — 



