POPULAR MISCELLANY. 



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the day ; but if breaks formed in the clouds, 

 the numbers began to rise, and the increase 

 was very much in proportion to the amount 

 of clear sky. It also appeared that these ab- 

 normal readings came more frequently with 

 auticyclonic than with cyclonic circulation. 

 The fact that during the days of abnormally 

 high readings the air did not become hazed 

 to anything like the extent indicated by the 

 number of particles, seemed to suggest that 

 these nuclei are of molecular dimensions, and 

 it is even possible they may not be nuclei at 

 all while the air is dry, and form nuclei in 

 saturated air. The Kingairloch observations, 

 when arranged in tables, showed that nearly 

 double the number of particles are required 

 to produce the same amount of haze when 

 the air is very dry as when it is damp. The 

 transparency of the air was also noticed to 

 be roughly proportional to the wet bulb de- 

 pression. It is not the amount of vapor in 

 the air that produces this effect, but the 

 nearness of the vapor to the dew point, which 

 seems to enable the dust particles to condense 

 more vapor by surface attraction and other- 

 wise, whei'eby, by becoming larger, they have 

 a greater hazing effect. In all densely in- 

 habited areas the air loses its purity, and in 

 all uninhabited areas it tends to regain it ; 

 but all uninhabited areas are not equally 

 good purifying ones. Much of the dusty im- 

 purity discharged into our atmosphere from 

 artificial sources, by volcanoes, and by the 

 disintegration of meteoric matter, falls to 

 the ground, but much of it is so fine it will 

 hardly settle. The deposition of vapor on 

 these small particles seems to be the method 

 adopted by Nature for cleansing them away ; 

 they become centers of cloud particles and 

 ultimately fall with the rain. 



The Labors of a Woodpecker. John B. 

 Smith, of Rutgers College, New Jersey, writes 

 to Garden and Forest that he has received a 

 piece of white oak, thirteen inches in length 

 and three inches in diameter, containing four 

 holes made by a woodpecker. Each of the 

 holes is nearly or quite an inch wide with 

 the grain, and a trifle less across the grain, 

 narrowing to the bottom of the holes ; each 

 of them reaches into the center of the tree 

 and into an insect burrow. In order to reach 

 one of the larva3 which were the object of 

 its researches, the bird was compelled to 



make two attempts, having missed the point 

 on the first attempt. The larva for which 

 all this work was done measured about three 

 quarters of an inch in length, with a diame- 

 ter of perhaps one sixteenth of an inch, and 

 would hardly serve to make more than a 

 scant mouthful for even the smallest wood- 

 pecker. It must have taken the bird at least 

 half an hour of persistent work to make each 

 hole, or at least an hour to secure this one 

 larva, weighing only a few grains. It seems, 

 Mr. Smith remarks, as if it would be almost 

 impossible to gain from such a larva a fair 

 return in food value for the energy exjiend- 

 ed in getting at it, especially where it is ne- 

 cessary to make two efforts to recover one 

 mouthful. In the other burrows the bird was 

 more successful, and gained the larva at the 

 first attempt. 



A Forest in Nicaragaa. With the excep- 

 tion of a few clearings, the entire region of 

 the San Juan River, Nicaragua, is described 

 by B. Shimek, in his report to the Natural 

 History Society of the State University of 

 Iowa, as covered with typical tropical forests. 

 They are almost impenetrable, except with 

 the aid of the machete, with which the trav- 

 eler must literally tunnel his way in many 

 places through the walls of vegetation. The 

 trees, many of which are very tall and from 

 eight to fourteen feet in diameter, are not 

 quite so closely placed together as those of 

 our northern forests ; but the intervening 

 spaces are covered with shrubs and vines and 

 numerous other plants, so that, particularly 

 in lower places, dense jungles are formed. 

 Moreover, each tree is a veritable garden in 

 itself. The masses of parasites and epiphytes 

 which cover the larger branches of the trees, 

 and often extend down the trunk and along 

 the smaller branches to their very tips, form a 

 perfect canopy overhead through which the 

 sun's rays never penetrate. Ferns, brome- 

 lias, orchids, mosses, and many other plants 

 crowd their hosts with a dense mass of multi- 

 colored vegetation. In their active struggle 

 for existence with more powerful neighbors 

 of the forests, these plants have probably 

 gradually ascended, in their search for the 

 sun's light, to the upper branches of the very 

 neighbors which sought to crowd them out, 

 thus transferring the struggle from the sur- 

 face of the soil: to the air above. So firmly 



