May 2, 1907] 



NA TURE 



freely move about, whereas when it is cold and rigid such 

 freedom of movement is impossible ; in consequence the 

 definite formation of crystals cannot take place, and the 

 result of the change is different. What happens is this. 

 In the first place, molecules of the same kind tend to 

 separate out from the homogeneous mixture and collect 

 round a point, forming a centre of decomposition. Pro- 

 ceeding from this centre the glass is found decomposing 

 into definite compounds in an ever-enlarging circle until 

 it reaches a point at which the strain set up in the glass 

 by this molecular movement results in a crack forming 

 round the area of decomposition, and then the whole mass 

 comes away, leaving behind it a little hole or pit in the 

 surface of the glass. 



Such are the two forces at work on the decay of glass — 

 corrosion without and decomposition within — and, of 

 course, they act simultaneously. As the pits are formed 

 they are extended by corrosion, forming a resting place, in 

 fact, for the water, until eventually the whole fabric of the 

 glass is destroyed. 



According to varying circumstances — the position of the 

 window as affecting its degree of exposure, the climate 

 in which it is placed, differences in composition and 

 mechanical state of the glass — we get all sorts of variations 

 in the precise effect of decay in particular instances. 



It is a well recognised fact that glass containing a large 

 proportion of earths, that is, lime, magnesia, and alumina, 

 is especially liable to become crystalline. If, then, one is 

 correct in thinking that the peculiar pitting of Gothic 

 glass is due to a similar change of constitution, one would 

 expect to find it excessively rich in these constituents, 

 and we have already seen that this is, in fact, the case. 



On the other hand, glass containing excess of alkali has 

 an equally recognised tendency to go " blind," that is, to 

 become covered with a film, due to corrosion. Finally, 

 glass with a high content of silica, with earth and alkali 

 equally balanced, may be looked upon as highly resistant 

 in both directions. It is such glasses which decay slowly 

 and with little tendency to devitrification, the surface being 

 merely etched by corrosion, leaving the large proportion 

 of silica in a coherent thin film, producing gorgeous effects 

 of iridescence. 



Besides the glass itself, a study of the materials used 

 for producing the enamel with which the glass was painted 

 to represent figures and subjects is a matter of some 

 importance, which is fully discussed in the paper. After 

 going thoroughly into the evidence afforded by those 

 mediaeval pay-rolls which have been preserved, dealing with 

 the execution of stained-glass windows, the author comes 

 to the conclusion that the enamel in question was prepared 

 by making a fusible opaque black glass, technically known 

 as " geet," probably because it resembled jet in appear- 

 ance (the word jet being in writings of the period variously 

 spelt jeat, ieat, geat, goet) : this material would be used 

 as a flux, and mixed with the oxides of iron and copper 

 to make the paint. Experiment shows that an enamel 

 prepared in this way is in every respect similar to that 

 used in the finest examples of mediaeval stained glass. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



.'\n exhibition illustrating a course of lectures on 

 Japanese education given under the auspices of the Uni- 

 versity of London by Baron Kikuchi, will be opened on 

 Tuesday next at the Victoria and Albert Museum (Indian 

 Section), South Kensington. The exhibition will remain 

 open until the end of June. 



Recent statistics published by the French Minister of 

 Public Instruction give the number of students attending 

 courses of instruction in French universities and higher 

 educational institutions. The total reaches 38,197, of 

 whom 3434 are foreigners — a number much larger than 

 usual owing to the temporary closing of certain Russian 

 universities. Of the native students, 1364 are women. 

 The number of students at some of the larger universities 

 are as follows : — Paris, 15,789 ; Lyons, 2783 ; Toulouse, 

 2675 ; Bordeaux, 2496 ; Nancy, 1841 ; Montpellier, 1752 ; 

 Lille, 1560; Rennes, 1498; and Aix-Marseilles, 1269. The 



NO. 1957, VOL. 76] 



Paris students are distributed among the different faculties 

 and schools as follows : — law, 7032 ; medicine, 3369 ; 

 letters, 2413 ; science, 2022 ; and pharmacy, 953. The 

 total number of French university men students include 

 in the various departments of learning: — law, 15,427; 

 medicine, 7501 ; letters, 4605 ; science, 5881 ; and 

 pharmacy, 2224. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, November n;, igofi —"On the Effect of High 

 Temperatures on Radium Emanation and its Products." 

 By Walter Makower and Sidney Russ. Communicated 

 by Prof. A. Schuster, F.R.S. 



In a previous paper it was shown that the activity of 

 radium emanation sealed in a quartz tube is temporarily 

 changed by subjecting it for a short time to temperatures 

 between 1000° C. and 1200° C. From the results obtained 

 it seemed probable that this change was not due to any 

 alteration of the emanation itself, but rather to a change 

 of activity of one of the more quickly decaying products 

 of the emanation with which it is in equflibrium. To 

 settle this point measurements were made of the rate of 

 decay of the emanation when kept at 1100° C. Sub- 

 sequently experiments were made on the effect of high 

 temperatures on the active deposit collected on a platinum 

 wire by exposure to the emanation. 



The results obtained were : — 



(i) The change in activity noticed when radium eman- 

 ation is subjected to a high temperature is not due to any 

 alteration in the emanation itself, since its time period 

 is unaltered when it is maintained at a temperature of 

 1100° C. 



(2) The change is due either to a change in radium B 

 or C, since the activity of a mixture of these two sub- 

 stances can be changed by heating. 



(3) The change is probably due to some influence of 

 temperature on radium C. This conclusion is in agree- 

 ment with the statement made by Curie and Danne. 



In a note the authors discuss some recent observations 

 made by Dr. Bronson which appear at first sight difficult 

 to reconcile with the above conclusions. As a result of his 

 experiments. Dr. Bronson concludes that there is no change 

 of activity in radium even when exposed to temperatures 

 of 1600° C. 



It is, however, pointed out by the authors that there 

 are seveial important differences between Dr. Bronson 's 

 experiments and their own, the most important of which 

 is that Dr. Bronson measured the activity of the radium 

 while hot, whereas they always allowed the active deposit 

 to cool before making measurements. It is on this account 

 that the authors consider that the results of Dr. Bronson 

 and their own are not necessarily contradictory. 



Zoological Society, April 9. — Dr Hfnry Woodward, 

 F.R.S., vice-president, in the chair. — A collection of fishes 

 made in the eastern watershed of the Transvaal by Captain 

 G. E. Bruce, and presented to the British Museum : G. A. 

 Boulenger. The collection contained specimens of 

 eighteen species, of which several had not been previously 

 recorded from the Transvaal, and five were new. — The 

 osteology of the oligomyodian and diacromyodian Passeres : 

 W. P. Pycraft. After referring to his previous contribu- 

 tion (published in the Proceedings) on the osteology of the 

 ouryL-emid and tracheophone Passeres, the author remarked 

 that there seemed little room for doubt but that the 

 diacromyodian and oligomyodian Passeres must be regarded 

 as divergent branches of a common stem. The latter sub- 

 order included the Tyranniformes, Phytotomida;, and 

 Pittidse, while the former embraced the remaining Passeres. 

 In the present communication some fourteen families were 

 described, and these were divided into four groups, Hirun- 

 dines, Muscicapae, Laniinje, and Gymnorhinje. This 

 arrangement was based, not on osteological characters 

 alone, but also on the evidence of pterylosis and certain 

 wing-muscles. The author proposed to include the 

 Vireonidae with the Muscicapa?, and the Vireolaniidae with 

 the Gymnorhinje. With this last group he proposed, 

 tentatively at any rate, to include the Paradiscida', 



