54 



NATURE 



[May 17, 1888 



May 5, 4 a.m., near Grossenhain, Saxony. 



,, 5, Island of Riigen, on the Baltic. 



,, 6, near Freiberg, Saxony. 



,, 6, near Konigstein, Saxony. 



,, 6, near Rendsburg, Holstein. 



,, 7, Reichenau, Saxony. 



,, 7, near Soldi n, Brandenburg, Prussia. 



,, 7, Palczyn, Posen, Prussia. 



,, 7, near Leipzig, Saxony. 



Royal Zoological Museum, Dresden, May 12. 



A. B. Meyer. 



" Coral Formations." 



In a recent paper read before the Royal Society of Edinburgh, 

 I have pointed out the importance of taking into consideration 

 the molecular condition of carbonate of lime in relation to its 

 solubility in sea-water. 



The (tabulated) results of an exhaustive series of tests (see 

 Nature, vol. xxxvii. p 605) show in a striking manner this 

 difference between the crystalline (or massive) and the 

 amorphous conditions of that body. 



In Table II. the amount of carbonate of lime taken up by sea- 

 water from decomposing shell-fish is shown to be very great, the 

 clear newly filtered solution giving 0*384 grammes per litre 

 (other determinations since made giving still higher results) ; 

 this is due no doubt to the formation of carbonic acid, the result 

 of the oxidation of the organic matter in the putrefying mass. 



The clear (foul-smelling) liquid on standing exposed to the air 

 rapidly decomposes, ammoniacal salts being formed ; and a great 

 portion of the amorphous carbonate of lime which was dissolved 

 during the first stages of putrefaction is thrown out of solution 

 and deposited in a crystalline and practically nearly insoluble 

 form. 



This may be due to the loss of carbonic acid, or its com- 

 bination with ammonia, produced during decomposition of 

 nitrogenous organic matter ; or to the well-known action certain 

 salts of ammonia (especially the carbonate) exert in degrading 

 the solubility of carbonate of lime in water ; but the result so 

 produced, I think, meets all the objections Mr. T. Mellard 

 Reade brings forward against the solution theory, which is Dr. 

 Murray's explanation of the formation of coral lagoons. 



Again, when a clear saturated solution of amorphous carbonate 

 of lime in sea- water (see Table II. , a and b) is allowed to stand for 

 a few hours at ordinary temperatures, the solution becomes 

 turbid and ultimately throws out in a crystalline condition a 

 considerable proportion of the carbonate of lime it held in 

 solution. 



Dr. Murray, in a paper on " Structure, Origin, and Distribu- 

 tion of Coral Reefs, &c.," read before the Royal Institution, 

 London, on March 16, refers to this change of condition as 

 follows : — 



" The whole of a coral reef is permeated with sea- water like a 

 sponge ; as this sea-water is but slowly changed in the interior 

 parts it becomes saturated, and a deposition of crystalline car- 

 bonate of lime frequently takes place among the interstices of the 

 corals and coral debris." 



These facts seem to me quite sufficient to account for the 

 formation of coral lagoons by the more rapid solution of the 

 amorphous form of carbonate of lime, found in dead and decom- 

 posing corals. At the same time other deposits are preserved 

 from wholesale solution by the change in the molecular condition 

 which carbonate of lime undergoes, — always the after result of 

 solution. 



I need not here refer to other influences at work in maintain- 

 ing the balance of absorption and secretion of lime salts in the 

 ocean, because I consider the difference in solubility of various 

 forms which carbonate of lime assumes equally accounts for the 

 formation of lagoons and the preservation of coral reefs and shell 

 beds or banks. Robert Irvine. 



Royston, Granton, Edinburgh, May 14. 



Aurora Borealis. 

 The aurora borealis was visible here on Sunday night, May 6. 

 We have difficulty in identifying it in this neighbourhood with- 

 out spectroscopic aid, because the lights of Liverpool and its 

 suburbs extend over the eastern horizon, and the sky to the 

 north-east and north is filled with a glow from Bootle and 



Birkenhead, these several lights often giving, with clouds "of 

 varying height, effects resembling northern lights. 



On Sunday night, at 1.30, the brightness in the north-western 

 sky was not to be mistaken ; and shortly before 2 o'clock a 

 curved bluish-white beam — two brilliant sides inclosing a still 

 brighter rounded angle of about 70 — shot up from the west, the 

 apex coming first, and attaining a height of 6o°, the sides there 

 being about i° broad ; the extremities of the sides, i° broad, 

 touching the horizon in the north-north-west and south-south- 

 east. This beautiful beam remained a few seconds, then went 

 as it came, the apex disappearing last. The general phenomenon 

 seemed to increase in brightness, but subsequent observations 

 show that it could not then be satisfactorily distinguished from 

 the early dawn and reflected lights. L. J. H. 



Rock Perry, May 11. 



Weight and Mass. 



The tveight of a body is the quantity which is measured out 

 by the operation of weighing. To weigh a body it is placed in 

 one of the scales of a balance, and equilibrated by standard 

 weights formed of lumps of metal called pounds, hundred- 

 weights, tons, &c, or kilogrammes in the metric system ; and 

 the sum of these weights is {pace Mr. R. E. Baynes) called the 

 zveight of the body. 



The mathematician may now call this quantity, if he likes, 

 the mass of the body ; but the world at large uses the word 

 weight, with the advantage of having the corresponding verb 

 "to weigh," which the substantive "mass" does not possess : 

 we are not yet accustomed to speak of a body " massing " 100 

 tons. The numerous circumlocutions to express one single idea 

 in Prof. MacGregor's examples arise from the want of the verb 

 " to mass." 



The " extraordinary and peculiar " language is, then, that of 

 the elementary text-books of Mechanics, which tell us that the 

 weight of a body is the force with which it is attracted by the 

 earth (Lodge, " Elementary Mechanics," p. 66). 



It is true, as Sir Philip Magnus points out in his " Mechanics," 

 § 46, that the word weight is made to do double duty, sometimes 

 standing for force a id sometimes for mass ; and that these two 

 significations must be carefully distinguished. 



But the "ordinary he or she" would no more accept the 

 " pull or heft required to lift a body" as a correct measure of 

 the weight, than the Red Indian of to-day would accept the 

 weight of the Hudson Bay factor's fist as one pound. 



The theorist must then exert his ingenuity to invent a new 

 word to express the force idea, to associate with the word mass, 

 already invented by him ; but to attempt to restrict the meaning 

 of the word weight in a manner not usual in ordinary language 

 can only lead to confusion. In any engineering, chemical, or 

 ordinary journal we shall always find weight used in the sense 

 of mass, as defined in the text-books of elementary dynamics ; 

 and even in these treatises we shall find in the parts on Statics 

 the word weight used in its ordinary sense. For instance, on 

 p. 196 of Dr. Lodge's "Mechanics," we find, Ex. 10, "A mass 

 of wood (sp. gr. o'6) is counterpoised by 105 correct grammes 

 of iron (sp. gr. 7*5); find the mass of the wood (or its true 

 weight in vacuo)." 



Sometimes it is not possible to employ the balance to estimate 

 the weight (or mass) of a body ; as, for instance, when the 

 chemist evolves a certain weight of hydrogen in a chemical com- 

 bination, when the artillerist speaks of a gun 'weighing no 

 tons, and when the astronomer "weighs the earth," — in such 

 cases the weight or mass, whichever it is called, is calculated as 

 the product of the volume and the density : determine for 

 example the weight of 1000 cubic feet of steel. The weight W 

 (or mass M) is then found theoretically from the formula W (or 

 M) = pV, but really practically from the formula W = 62 '4-fV, 

 where W or M is given in pounds, when V is given in cubic 

 feet, and p is then called the density, and s the specific gravity 

 (the density relative to water), and it is the specific gravity for 

 which tables are given ; but in the metric system W (or M) = 

 pV = sV, where W or M is given in grammes, when V is given 

 in cubic centimetres, and the density p, and the specific gravity s, 

 are then the same. But turn to the ordinary text-books, and we 

 find these confusing equations — 



W = Mg = g P V = sV, 



where W is called the weight, M the mass, p the density, and f 

 the specific gravity, followed oftenby a series of absurd examples 

 on changes of units. 



