HARDWICKE'S SCIENCE-GOSSIP. 



155 



any acidity in the food passed on from the crop. It 

 emulsities fats, wliich is only temporarily done by the 

 saliva, and converts albuminoids into peptones.* 

 The secretion of the glandular wall of the chylific 

 stomach could not be satisfactorily Isolated. (5) 

 There are no absorbent vessels, the products of 

 digestion passing by osmosis through the wall of the 

 digestive tube to mingle with the blood which circu- 

 lates in the perivisceral space. 



GOSSIP ON CURRENT TOPICS. 



IN the last and previous numbers of Science - 

 Gossip are some letters on domestic aquaria, 

 the appearance of which is refreshing, as the little 

 tanks seem to have been snuffed out recently by the 

 larger displays of the public aquaria which they 

 preceded and suggested. So much interest, in- 

 struction, and elegance is afforded, even by a very 

 small well-managed aquarium at home, that a revival 

 of the popularity of such humble "zoological stations " 

 is very desirable. 



A remark of Mr, Walter T. Cooper, respecting 

 the "poisonous matter" contained in Portland 

 cement, indicates that an explanation of the chemistry 

 -of this is demanded. When the Crystal Palace 

 aquarium was started I was consulted by my old 

 friend Mr. Lloyd, with whom I had co-operated in his 

 early small attempts, concerning a dilemma in which 

 he found himself. The building was complete ; his 

 admirable duplicate arrangements for circulating the 

 water throughout the tanks were all in order ; the 

 tanks were filled with water from Brighton, and the 

 stocking with animals had commenced in good time 

 for the opening as announced, but, alas ! the water, 

 at first quite clear and bright, gradually became 

 turbid, and the animals simultaneously sickened and 

 died. 



On examination, I found it slightly alkaline, and 

 thus at once indicated the cause of the trouble. 

 Portland cement contains caustic lime, i.e. lime 

 in its alkaline condition. Such lime is soluble in 

 either river or sea-water, and when these contain, as 

 they usually do, some carbonate of lime dissolved in 

 excess of carbonic acid, the caustic or alkaline lime 

 combines with this excess, and is not only itself 

 precipitated as insoluble carbonate of lime, but also 

 effects a further precipitation of the carbonate of 

 lime that existed originally in the water dissolved by 

 its free carbonic acid. 



I accordingly proposed that hydrochloric acid 



* This was first demonstrated by Jousset de Bellesme, who, 

 however, erroneously states that the secretion is acid ; it is really 

 alkaline, like the proteolytic secretions of the pancreas of 

 mammalia. Plateau uses the muscles of the fly for digestion by 

 the chylific fluid of the cockroach, and finds that the micro- 

 scopic characters of the fibres render it easy to judge by simple 

 inspection of the progress of the digestive process. 



should be carefully added, and proved its efficacy by 

 clearing the water of an experimental tank. I also 

 suggested that by allowing sufficient time, and keeping 

 up a vigorous circulation of the water, the carbonic 

 acid of the air would eventually do the work of 

 clearing. Mr. Lloyd, having a dread of artificial 

 chemicals, preferred this method, which was adopted 

 with complete success, but it delayed the stocking 

 of the tanks by some weeks. 



The lecture delivered by Professor Osborne 

 Reynolds, at the Royal Institution, on Friday, 

 March 2Sth, is very interesting and instructive. It 

 is an able popular exposition of a somewhat difficult 

 mathematical subject, and supplies a lesson not only 

 to those for whom it is directly intended, but also to 

 the especially special mathematical specialists, who 

 fall into the sin of mathematical self-righteousness by 

 assuming, as a matter of course, that mathematical 

 demonstration settles everything. 



Professor Reynolds commenced by saying that 

 "in spite of the most strenuous efforts of the ablest 

 mathematicians, the theory of fluid motion fits very 

 ill with the actual behaviours of fluids, and this for 

 unexplained reasons. The theory itself appears very 

 tolerably complete, and affords the means of calcu- 

 lating the results in almost every case of fluid motion, 

 but while in many cases the theoretical results agree 

 with those actually obtained, in other cases they are 

 altogether different." He then proceeds to show 

 how the theory stands experimental verification 

 when applied to a raindrop falling through the air, 

 but fails in the case of a large body, such as a ship 

 moving through the water, and affords ' ' no clue to the 

 reason why it should apply to the one class more 

 than to the other." We have here an example 

 illustrating the absolute necessity of verifying by 

 observation or experiment every theoretical con- 

 clusion that falls within the reach of such verification, 

 without which it is merely an hypothesis and should 

 be scrupulously described accordingly. 



The calculations of Adams and Leverrier, which 

 led to the'discovery of the planet Neptune, are justly 

 regarded as great triumphs of mathematical reasoning, 

 but it is an error to assert, as commonly done, that 

 these mathematicians discovered the planet. What 

 they actually did was to formulate an hypothesis to 

 account for certain observed perturbations of Uranus, 

 which might be due to the gravitation of an outer 

 planet having certain positions at given times. The 

 actual discovery by the telescope proved the truth of 

 the hypothesis. Subsequently Leverrier based upon' 

 similar mathematical measurements of the perturba- 

 tions of Mercury the hypothesis of an inner planet, 

 and calculated its hypothetical orbit, but it is now 

 fairly evident that this planet Vulcan is but a mathe- 

 matical fiction, though the mathematical demonstra- 

 tion of its existence is as good as was that of the 

 existence of Neptune prior to its actual discovery. 



Unappreciated discoveries are common enough, 



