8c6 



THE POPULAR SCIENCE MONTHLY. 



left them to wander around the garden, only 

 returning to give them suck She at length 

 escaped from the garden to Neuilly, but re- 

 turned of her own accord. For fear of los- 

 ing her entirely, she was separated from her 

 young and fastened up. The young are 

 very familiar, and play all day long with the 

 other young dogs. 



Thrifty Birds. A curious illustration of 

 the industrial instincts of animals, given in 

 M. Frederic Houssay's book on that subject, 

 is afforded by the California woodpecker, 

 which, though an insect eater, stores away 

 for its winter supply food of an entirely dif- 

 ferent character, not so subject to decay. It 

 collects acorns, for which it hollows small 

 holes in a tree a hole for an acorn into 

 which the acorn is exactly fitted, ready to 

 be split by the strong beak of its owner, but 

 too tightly held to be stolen by other birds 

 or squirrels. Another woodpecker, in Mex- 

 ico, stores against droughts, selecting the 

 hollow stem of a species of aloe, the bore of 

 which is just large enough to hold a nut. It 

 drills holes at intervals in the stem and fills 

 it from bottom to top with nuts, the separate 

 holes being probably made for convenience 

 of access to the column of nuts within. The 

 common ants of Italy store oats and other 

 kinds of grain in chambers which they make 

 of about the size of a watch. They have a 

 way of keeping the grains from sprouting 

 with which we are not acquainted ; and if 

 they are removed, the seeds sprout. When 

 they wish to use their store, they allow the 

 grains to germinate till the chemical change 

 takes place in the material that makes its 

 fermenting juice suitable for their digestion. 

 They then arrest the process of change by 

 destroying the sprout, and use the stock 

 of glutinous sugar and starch as their main 

 food in winter. 



Atmospheric Dust and Air Colors. Hav- 

 ing continued his observations on dust parti- 

 cles in the atmosphere in connection with 

 other meteorological phenomena, Mr. John 

 Aitken has now exceeding fifteen hundred 

 observations, to produce which required the 

 testing of fifteen thousand samples of air. 

 The list includes, besides Great Britain, ob- 

 servations made in the south of France, at 

 Hyeres, Cannes, and Mentone, and at the 



Italian lakes. At none of the places in these 

 districts was pure air ever met with. On the 

 slopes of Monte Motterone, at Baveno, with 

 the wind blowing up the slopes and carrying 

 up the impure air, the amount of dust at 

 two thousand feet was reduced only to 0'64 

 of the number at low level, while if the wind 

 was from other directions it was reduced to 

 0'3. The conclusion that the descriptions 

 given by many writers of the beauty of the 

 coloring on earth and sky seen at high level 

 at sunrise and sunset are much exaggerated 

 is confirmed by the observations on the Rigi 

 Kulm. During five years no coloring at sun- 

 rise or sunset was witnessed from this point 

 equal to what is frequently seen at low level. 

 The sunset colors are shown to depend very 

 much on the amount of dust in the air. 

 When the atmosphere is comparatively free 

 from dust the coloring is cold, but the light- 

 ing is clear and sharp ; and when there is 

 much dust, there is more color on the moun- 

 tains and clouds and in the air itself, and 

 the coloring is warmer and softer. At high 

 level the coloring is more feeble and of 

 shorter duration. A thick veil of haze seemed 

 to hang in the air between the observer and 

 the mountain on all days when the number 

 of particles was great, and it became very 

 faint when the number was small. The con- 

 dition of the air on the occasions of the dif- 

 ferent visits to the Rigi varied greatly. The 

 clearest days, with the lowest numbers of 

 particles, were when the wind blew from the 

 Alps. The daily maximum on the Rigi did 

 not appear on all days. Winds from pure 

 directions generally prevented it, either by 

 checking the ascent of the valley air, or by 

 the valley air being pure, or by the pure val- 

 ley air not being much heated by the sun 

 and therefore having but little tendency to 

 rise. It was very marked when the wind 

 was from the plains. The hour at which the 

 rise in numbers began and the hour of maxi- 

 mum were very irregular. The amount of the 

 daily maximum varied greatly ; sometimes it 

 was only two or three times the morning 

 number, while it at other times exceeded it 

 eightfold. In the observations at Kingair- 

 loch, in Argyllshire, certain abnormal read- 

 ings of dust particles were always accom- 

 panied by certain conditions of weather. If 

 the sky remained clouded all day, the num- 

 bers were always low during the whole of 



