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THE POPULAR SCIENCE MONTHLY. 



the flame of the explosion had not extended 

 thus far. The walls of the galleries had 

 been swept clear of timber, and presented 

 the appearance of having been brushed 

 with a broom. Volumes of coal-dust had 

 been driven along by the force of the blast, 

 and lay in waves and drifts on the floor of 

 the levels, into which the party sank to 

 their knees. It was found that clouds of 

 the finer particles had been carried to the 

 shaft and beyond it into the main north 

 level, where a secondary explosion had taken 

 place. . . . Secondary explosions caused 

 by extracted or generated gas are nearly 

 always in the vicinity of the first one ; but 

 here is a case where the second was half a 

 mile from the first, with an intervening 

 space of at least a quarter of a mile known 

 to have been free from flame and presumed 

 to be free from gas, because men were in it 

 with lamps which showed no indications of 

 its presence." The conclusion is drawn that 

 the fine dry particles were driven on by the 

 force of the first explosion across the shaft, 

 where the dampness preserved them, iDto 

 the "lamp-cabin," where they were readily 

 ignited by the lamp which was kept burn- 

 ing openly, and thus caused the second ex- 

 plosion ; " and it is probable that the same 

 agency was efficient in producing, or at least 

 augmenting, the subsequent explosions that 

 made it necessary to flood the whole mine." 

 A competent explanation on chemical prin- 

 ciples of the remarkable exhibition of force 

 and heat accompanying dust-explosions is 

 needed. 



Significance of Ancient Masons' Marks. 



Professor Franz Rziha, of Vienna, has 

 published the results of investigations, to 

 which he has devoted many years, into the 

 origin and meaning of the masons' marks 

 which arc frequent in the constructions of 

 antiquity and the middle ages, and which he 

 specifies as occurring in Grecian, Roman, 

 and Syrian buildings, as well as in later 

 ones. They have been regarded as mystic 

 signs, arbitrary marks, private signs, or 

 simply as letters. Professor Rziha believes 

 that they had a far wider significance, and 

 that they formed, before the now recog- 

 nized laws of statics on which the building 

 art rests were made known by Galileo, the 

 means by which the master transmitted to 



his students the secrets of his art, and to 

 his workmen the principles of his plan. 

 Particular figures were employed as a kind 

 of a graphic key to the conditions of a con- 

 sistent structure. The circle, square, cross, 

 and triangle furnished the four elements of 

 graphic delineation ; the compass, rule, and 

 square were the three tools absolutely nec- 

 essary to guide the work, and were indis- 

 pensable in securing the proportions best 

 adapted to give strength to all parts of the 

 building. The geometrical properties and 

 relations of the figures used thus served to 

 indicate the proportions that were to be ob- 

 tained. Professor Rziha maintains that the 

 figures were never arbitrary, but that they 

 were always derived from and conformable 

 to common geometrical types. A comparison 

 of more than five thousand masons' marks 

 which he has made shows that, however 

 independently individual signs may have 

 been chosen, the combination of the lines is 

 subject to a law in the shape of a geometrical 

 pattern, of which the lines, whether straight 

 or curved, must be a part. He has traced 

 out some of these original designs, and has 

 been able to adapt the lines of the marks 

 to them without any artificial straining 

 in strong confirmation, he believes, of his 

 theory. After reviewing the modifications 

 which these marks underwent in time and 

 in different countries, Professor Rziha shows 

 how it is possible to ascertain from them 

 the ages at which buildings were erected. 



Physiological Immunities of the Jews. 



The "Revue Scientifique " has drawn the 

 conclusion, from a comparison of the vital sta- 

 tistics of different countries, that the Jews 

 nearly everywhere enjoy certain physiolog- 

 ical immunities which distinguish them from 

 the other inhabitants, among which are the 

 following : their general fecundity (propor- 

 tion of births to the whole number) is less ; 

 while the relative fruitfulncss of their mar- 

 riages to those of other races varies in differ- 

 ent places ; a greater proportion of their chil- 

 dren survive everywhere ; illegitimate births 

 and still-born children arc more rare among 

 them ; the proportion of males to females 

 among the births is greater; their mor- 

 tality is lighter, the mean duration of life 

 is greater; they increase more rapidly by 

 the excess of births over deaths ; while they 





