86o 



THE POPULAR SCIENCE MONTHLY 



and by which their foot-prints are distin- 

 guished, are wholly absent from the im- 

 pressions. The absence of any evidence 

 that the maker of the tracks had more than 

 two feet is also insisted upon. " The curve 

 of the foot is so regular and so constant as 

 to show that in every instance the hind- foot 

 if of a quadruped was at all times placed 

 exactly upon the forward foot, or that both 

 the forward and the hind feet were of ex- 

 actly the same form conditions which, to 

 say the least, are extremely improbable." 

 Evidence appears to be afforded in the 

 shape of the tracks of one or two of the 

 series that they were made by a yielding 

 material which, like leather softened by 

 moisture, gave way and was bent up at the 

 sides. Unless something of this kind is ad- 

 mitted, the tracks must be believed to have 

 been made by animals of different species. 

 Other variations in the shapes of the tracks 

 may be more readily accounted for by sup- 

 posing them to have been made by sandals 

 of different cuts than by quadrupeds hav- 

 ing differently shaped feet. Dr. Harkness 

 accounts for the width of the straddle, 

 which has been urged against the human 

 origin of the tracks, by suggesting that it 

 would be cue of the natural results of the 

 exertion of walking in mud with the feet 

 encumbered by such an unwieldy load as 

 the enormous sandals. 



Hygienic Qnalities of Electric and Gas 



Lights. Mr. B. H. Thwaite suggested, some 

 years ago, that the intense heat developed 

 in the arc electric light would produce a 

 rearrangement in the gaseous contents of 

 the atmosphere, by changing a mechani- 

 cal combination into a chemical one, with 

 the resultant development of deleterious 

 nitrogen oxides. Mr. Wills, F. C. S., showed 

 by experiment that ten to twelve grains 

 of nitric acid were developed in an hour 

 by the electric lamp. This rearrangement 

 of gases is not produced in the incan- 

 descent lamps, for, besides the less devel- 

 opment of heat, the filaments are kept in 

 a vacuum. Hence, per sc, the electric light 

 of the incandescent type is hygienically sat- 

 isfactory ; but neither the incandescent nor 

 the arc electric light assists vegetation. Be- 

 sides the nitrogen oxides produced by the 

 arc-light, says Mr. Thwaite, probably as 



much carbon dioxide is produced for the same 

 illuminating power as is produced by the 

 combustion of coal-gas. In both lights, the 

 luminosity proceeds from the same cause 

 carbon heated to incandescence. The light 

 produced by incandescent lamps is in almost 

 perfect accord with the laws of visual or 

 ocular hygiene, for it permits a choice of 

 colors, but the arc-light is not so satisfac- 

 tory, because* it induces fatigue by its vari- 

 ations and its glare. The products of the 

 combustion of coal-gas are aqueous vapor 

 and carbon dioxide, with sulphuric acid re- 

 sulting from the oxidation of the bisulphide 

 of carbon contained in the gas. Besides 

 these, nitrogen is set free from its mechani- 

 cal combination with oxygen, but it is prac- 

 tically harmless. These gases may be re- 

 moved by putting over the burners pipes 

 for conveying them to the open air ; and, if 

 this were done, as it ought always to be 

 done, the greatest disadvantage of the sys- 

 tem of coal-gas lighting would be removed, 

 and adequate ventilation would at the same 

 time be provided. With regenerative burn- 

 ers, the intensity of combustion could be 

 increased to such a degree that the light 

 would be white and neutral, permitting col- 

 ors of the most delicate hues to be easily 

 distinguished. We should then have a light 

 not only hygienically perfect, but, to the 

 extent that it is utilized for assisting venti- 

 lation, superior in that respect to the best 

 electric light. 



Aeration of Peaty Water. Professor 

 W. N. Hartley and Mr. Gerard A. Kinchan, 

 of Dublin, have made experiments with ref- 

 erence to the alleged power of aeration to 

 purify the water of rivers from peaty mat- 

 ter they may have in solution, from which 

 they are led to deny the existence of such 

 power to any measurable extent. Their first 

 experiment was made at the Powerscourt 

 Fall of the Dargle River, where the water 

 descends 300 feet vertically, and mostly in 

 the form of spray. Here, if anywhere, aera. 

 tion should have been general and effective ; 

 yet analyses of specimens from above and 

 below the fall showed no variation in the 

 amount of carbon beyond what could be 

 attributed to experimental error. Next, 

 samples of the water of Carawaystick Brook 

 were taken, from distances 1,600 feet apart, 



