July 29, 189; 



NATURE 



293 



Disappearance of Nitrates in Mangolds. 



During last autumn, winter, and spring, I made a series of 

 analyses of mangolds, determining in each case the nitrogen 

 present as albuminoids and as nitrates. 



The roots were pulled during the last week in October, and 

 clamped in the ordinary way. Roots of the same weight- 

 about 7 pounds— were taken for analysis on the dates shown in 

 the table. 



The albuminoid nitrogen was determined in the dry matter, 

 by leaving two grams in contact with 4 per cent, carbolic acid, 

 containing metaphosphoric acid, for twenty-four hours ; the 

 nitrogen determined in the insoluble portion, by Kjeldahl's 

 method, being taken as albuminoid nitrogen. 



The total nitrogen was determined by a modification of 

 Kjeldahl's method in the dry matter. 



The nitric nitrogen was determined in the juice by Schlcesing's 

 method. 



The amide and ammoniacal nitrogen was calculated from the 

 above by difference. 



The results are given in the annexed table. 



Table of Results of Mangold A nalyses. 



1 This root was rotten inside and hollow. 



Two questions appear to me to arise from these analyses : 



(i) Is the disappearance of the nitrates due to a denitrifying 

 action of the cells, or to bacterial action ? 



(2) Is not this disappearance of the nitrates during storage 

 answerable for the fact that mangolds are more suited for food 

 after January than in the autumn ? 



I purpo.se repeating these experiments on a larger scale next 

 winter. T. B. Wood. 



Agricultural Department, University of Cambridge. 



Globular Lightning. 



The following appears to be an instance of so-called 

 " Globular Lightning " (Nature, vol. xl. pp. 296, 366, 4i5,<S:c.). 



During the thunderstorm of July 20. with which the drought 

 broke up, an elderly man, Thomas Smith, residing in this parish 

 about half a mile from the railway station, was watching the 

 lightning from his cottage door, between 5 and 6 p.m., when 

 he noticed a white ball, "about the size of an egg," dancing 

 about in the air "like rooks when at play." He watched it 

 through the intervals between two or three lightning flashes, 

 therefore during several seconds. After some interval (perhaps 

 a few minutes), he still standing at the door, his wife just com- 

 ing down the stairs to him, something seemed to pass between 

 them which felt hot to their faces. Simultaneously Miss Downes, 

 schoolmistress, sitting on the landing above the stairs, felt some- 

 thing hot pass her hair behind, and then in a small bedroom, 

 with open door adjoining, a loud detonation took place ; white- 

 wash from the ceiling covered bed and floor, the wall-paper was 

 torn, the plaster fissured, and the house filled with a " sul- 

 phurous " smell. 



There is a draught up the stairs, but no apparent reason why 

 what it brought should enter the little bedroom. The cottage 

 stands alone, on high ground, but not the highest, and there is 

 nothing exceptional in its construction or its surroundings. 



Cockfield, Suffolk, July 22. E. IIil.l.. 



NO. 1448, VOL. 56] 



" Bicycles and Tricycles." 



In readmg Mr. Boys' most interesting review of Mr. Sharp's 

 book on "Bicycles and Tricyles " (Nature, July 8), a few 

 points occur to me as requiring further notice. 



In Chapter xi. , on bending, the strengths of tubes of various 

 sections are compared by considering the modulus (Z) of each 

 section, while Mr. Boys speaks of stiffness, and mentions that 

 D tubing is i per cent stiffer than round tube of the same 

 weight and width. I venture to think that, in stating this, Mr. 

 Boys has overlooked the fact that, since the D section is unsym- 

 metrical about the longer axis, the ratio of its moment of inertia 



to that of round tube ( J- ) is much greater than the ratio of the 



/v \ 

 moduli 



(!)■ 



Thus the relative stiffness of D tube ( -^51? - j -23 ) is 

 \-l25o "^Z 



much 



greater than its relative strength ( ^ ^ = i '008 j. 



These values assume the D section to be semicircular, and the 

 tubes to be infinitely thin ; when the thickness is finite, the 

 round tube must have the thicker wall, and the mean diameter 

 becomes less than the mean radius of the semicircle, so that the 

 ratios become greater still. 



In practice the semicircular section is seldom used, a much 

 more square-shouldered shape being preferred, which, whilst 

 only slightly less stiff than rectangular tube of the same weight, 

 width and perimeter, is much less unsightly in appearance. 

 The actual advantage of D tube over round is found by experi- 

 ment to be from 30 per cent, to 40 per cent. 



It may be well here to draw attention to tests of various 

 fanciful sections (webbed, corrugated, &c.), which are published 

 from time to time, showing great apparent advantages over plain 

 tubing. In every case the test is made by supporting the tube 

 at the ends, and applying the load at the centre by means of the 

 ordinary knife-edge used for testing solid bars. The result is that 

 the tube wall is crushed in long before the real limit of bending 

 moment is reached, and the test merely indicates resistance to 

 local denting. To avoid this the tube should be as long as 

 possible, and the load distributed over a large area. 



Mr. Sharp's book is the first serious effort that has been made 

 to bring the cycle-maker into line with the rest of the engineering 

 profession. R. H. Housman. 



Mason College, Birmingham. 



I AM obliged to Mr. Housman for pointing out a slip of ex- 

 pression in my review of Mr. Sharp's book. I had not confused 

 the ratio of the I's for the ratio of the D's, but merely in- 

 advertently used the word " stiffness " in its colloquial and more 

 extended sense, so to include resistance to forces which would 

 seriously bend or damage, as well as to those which would 

 produce infinitesimal bending. 



While on the subject of strength or stiffness of thin tubes, it 

 may be worth while to point out that the complete theory of 

 bending, as applied to very thin tubes, is by no means included 

 in the usual formula ; and it is for this reason that properly 

 designed experiment is essential in extreme cases. 



C. V. Boys. 



" A Text-book of Histology." 

 My attention has been drawn to a review of my work on 

 histology, which appeared in your issue of May 20 ; and as 

 the review appears to me to be biassed, and amounts in fact 

 to a public attack on me as an histologist, I trust you will, 

 in fairness, give me the opportunity of as publicly defending 

 myself, by inserting this letter in your next number. 



Not one of the charges brought against the book can be 

 fairly substantiated. Your space will not admit of my travers- 

 ing more than a few of the points raised, but these will serve 

 as samples of the whole. 



(i) Your reviewer refers to a well-known excellent atlas of 

 histology, and contrasts the accuracy of the drawings with 

 mine. I deny the justice of his comparison : to take instances, 

 if any one will compare the drawings of the eye and cochlea 

 in my textbook with those of the same structures in the atlas, 

 he will speedily be convinced as to where the inaccuracy lies. 

 If the descriptions in the atlas referred to contained much that 

 was new at the time, I can only say that histology must have 



