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THE POPULAR SCIENCE MONTHLY 



plied, and soon the microscope showed some 

 of the rotifers to have revived, while others 

 remained motionless. The same slides 

 were again submitted to drying, the cover- 

 glass of one having been removed. Several 

 hours after moistening them, the next day, 

 only two rotifers were seen to be alive on 

 each slide. Again some twenty active roti- 

 fers were exposed to the hot sun during the 

 afternoon. These could not be revived the 

 following morning. From all this it would 

 appear that rotifers become inactive in 

 comparatively dry positions, and may be 

 revived by supplying moisture ; but, when 

 their own substance is actually dried up, it 

 is impossible to revive them, 



Inflnenee of Ammonia on the Color of 

 Flowers. Exposure to the smoke of a ci- 

 gar changes violet-colored flowers to green. 

 This change is due to the ammonia present 

 in tobacco-smoke. The general question 

 of the influence of ammonia on the colors 

 of flowers has been lately investigated by 

 Gabba, an ItaUan, his method being to put 

 a little ammoniacal solution in a basin, and 

 place a receiver over it containing the flower. 

 In this way blue, violet, and purple flowers 

 were changed to green, carmine-red flowers 

 to black, white to yellow, etc. The most 

 singular changes were presented by flowers 

 in which several tints are combined ; the 

 red lines changed to green, the white to yel- 

 low, and so on. After the flowers have un- 

 dergone these changes, if they are placed 

 in pure water, they retain their new colora- 

 tion several hours, and then gradually re- 

 sume their original hues. Gabba has fur- 

 ther observed that the flowers of aster, 

 which are naturally inodorous, acquire an 

 agreeable aromatic odor under the influence 

 of ammonia. When moistened with dilute 

 nitric acid they change from violet to red. 

 If inclosed in a wooden case, and exposed 

 to hydrochloric-acid vapor, they in six hours 

 assume a beautiful carmine red. 



Metal Roofs as Lightning-Condnctors, 



In a communication to the French Acad- 

 emy of Sciences, E. Nouel gives the results 

 of his observations, made at Vendome dur- 

 ing a very violent storm. The lightning on 

 that occasion struck some telegraph-posts 

 and three houses. In the case of the houses, 



Nouel found that the lightning followed the 

 sheet-zinc roofing (without damage) to the 

 spouts, and thence to the earth. The author 

 remarks that static electricity flows always 

 to the surface of bodies, so that a gutter 

 and its pipe, notwithstanding the thinness 

 of the metal, constitute an excellent electric 

 conductor, having less resistance than the 

 best lightning-rods ; that the thunder-bolt, 

 as a rule, falls only during heavy showers, 

 by taking advantage of the semi-communi- 

 cation with the earth offered by the verti- 

 cal series of rain-drops. The summary of 

 his conclusions is as follows: 1. It is pos- 

 sible, almost without expense, to protect 

 ordinary houses from lightning casualties 

 by establishing good metallic communica- 

 tion between the chimney-flues and roof, 

 through the gutters, and by trusting to the 

 rain to complete the communication to the 

 ground. 2. That, even for complete light- 

 ning-conductors, we should utilize as a con- 

 ductor the gutters and their pipings. 3. 

 That there is need in every case to wholly 

 replace the conductors of lightning-rods 

 with hollow pipes of the same mass and of 

 greater diameter. He decidedly rejects me- 

 tallic cords, because electricit)', always fol- 

 lowing the conductor's surface, only selects 

 or uses from this cord a small number of 

 its wires, which may be easily fused. 



A Botanic Garden for Chicago. The 



Commissioners of the South Park, Chicago, 

 have in contemplation the establishment of 

 a Botanic Garden on the following liberal 

 plan : First, there will be a botanic garden 

 proper, in which all indigenous plants of 

 the United States, and hardy species from 

 other countries, will be arranged, as far as 

 possible, according to their natural aflini- 

 ties, while hot-houses and green-houses will 

 be provided for the reception and display 

 of tropical plants. There will also be an 

 arboretum, or collection of hardy trees, from 

 all parts of the world, planted in such order 

 as to serve the purposes of science and or- 

 nament ; a garden devoted to floriculture ; 

 a botanical museum, for the exhibition of 

 vegetable economic products ; an herbari- 

 um, or collection of specimens of dried plants, 

 scientifically arranged ; finally, a library of 

 botanical works. The South Park com- 

 prises about 1,200 acres, and the commis- 



