from his results will be sufficient for our purpose, namely: "When the tension of the vapor was 0.888 inches the fall of the thermometer was 6.0° Fahr., and when the tension was only 0.435 inches the fall amounted to 16.5° Fahr." It is fair to state that these observations were conducted long before Tyndall's researches with aqueous vapor, and are on this account all the more valuable. The evidence we have adduced seems to show conclusively, that the vapor forms a sort of invisible canopy separating the chilling air above from the warm earth beneath, and arresting, more or less effectually, the radiation. We have a homely illustration of this when we see the thrifty housewife spread coverings over the more delicate plants of her flower garden on nights when she fears a frost. It has been said that aqueous vapor is a blanket more necessary to the vegetable life of England than clothing is to man; and every plant capable of destruction by freezing would succumb, if this vapor were removed for a single night. In support of this assertion it will be well to notice the results obtained by some noted observers concerning the daily fluctuation in temperature in other countries. Dr. Livingston has observed a great excess in nocturnal chilling when the air is dry over that which occurred when it is laden with moisture. He has found in the southern central portion of Africa, during the month of June, the thermometer early in the mornings at from 42° to 52° Fahr., at noon 94° to 96° Fahr., or a mean difference of forty-eight degrees between sunrise and mid-day. He says, furthermore: "The sensation of cold after the heat of the day was very keen. The Balonda at this season never leave their fires till nine or ten in the morning. As the cold was so great here, it was probably frosty at Linyanti; I therefore feared to expose my young trees there." Crossing the continent, Dr. Livingston reaches the Zambezi at the commencement of the year. He gives the following description of the change felt on entering the valley of the river:

We were struck by the fact that as soon as we came between the range of the hills which flank the Zambezi the rains felt warm. At sunrise the thermometer stood at from 82° to 86° Fahr.; at mid-day in the coolest shade, namely, in my little tent, under a shady tree, at 96° to 98° Fahr., and at sunset at 86° Fahr. This is different from anything we experienced in the interior.

1 Livingston's Travels, p. 484.

2 Livingston's Travels, p. 484.

Proceeding toward the mouth of the river (Jan. 16th), he makes the following additional observation:

The Zambezi is very broad here (at Zumbo) but contains many inhabited islands. On the 16th we siept opposite one called Shibanga. The nights are warm, the temperature never falling below 80°, it was 90° Fahr. even at sunset. One cannot cool the water by a wet towel round the vessel.1

Evidently the air was nearly saturated with moisture in the latter locality, and this affords the only explanation of the evenness of the temperature here.

In Australia the daily range of the thermometer is extremely great. The observations of Mr. W. S. Jevons are of much interest, and we give an extract:

* * *

In the interior of the continent of Australia the fluctuations in temperature are immensely increased. The heat of the air, as described by Capt. Stewart, is fearful during summer; thus in about latitude 30° 50′ S., and longitude 141° 18′ E., he writes: The thermometer every day rose to 112° or 116° in the shade, while in the direct rays of the sun from 140° to 150°." Again, “At a quarter past three, P. M., on January 21st (1845), the thermometer had risen to 131° in the shade and 154° in the direct rays of the sun. In the winter the thermometer was observed as low as 24°, giving an extreme range of 107°" From these data we are not surprised to hear him remark further on, that, "The fluctuations of temperature were often very great and sudden, and were severely felt." He says, moreover, "It thus appears that even close to the ocean the mean daily range of the Australian climate is very considerable. It is least in the autumn and greatest during the cloudless days in spring." After giving here a table of the seasonal variation of the rainfall in Australia, Mr. Jevons says that, "It is plainly shown that the most rainy season of the year on the east coast is the autumn, that is, the three months, March, April, May. The spring season appears the driest, summer and winter being intermediate.

Prof. Tyndall says: 3

Without quitting Europe we find places where, while the day temperature is very high, the hour before sunrise is intensely cold. I have often experienced this in the post-wagons of Germany; and I am informed that the Hungarian peasants, if exposed at night, take care, even in hot weather, to protect themselves by heavy cloaks against the nocturnal chill.

All this evidence should be sufficient to convince the most

1 Livingston's Travels, p. 575.

2 Quoted by Tyndall.

3 Discourse on radiation through the Earth's Atmosphere.

skeptical that aqueous vapor furnishes a very effectual barrier to terrestrial radiation.

The tropical torrents can be accounted for by the property vapor has to absorb and radiate heat, thereby condensing the vapor raised from the equatorial regions through the direct rays of the sun. But it is only the upper strata of the vapor bed covering the surface of the earth, which by radiating into open space produces the effect above stated. Owing to the same quality may be explained the formation of cumuli; the theory of sereim, or the falling of the exceedingly fine rain shortly after sunset in the fine season. These and many other meteorological phenomena receive their solution from the development of this property of aqueous vapor. Every one will readily acknowledge that a question affecting so materially important sciences as the one under consideration, should be quite definitely settled, and it is for this reason that so much stress, by way of testimony, has been here placed upon it.

Admitting then that the vapor in the air does, by the property above discussed, influence numerous climatic conditions, the sources of this vapor certainly should claim a larger share of

attention.

Nature's chief means of furnishing this moisture is through vaporization from the ocean, especially in the tropics; but many tracts of country inland, or even near the great seas, do not, for some reason, contain sufficient moisture. Now, if by any means at our command we can assist nature in supplying this very essential substance, it would be well worth our endeavors. Here the question presents itself, "Is there any connection, all things considered, between the proportion of moisture in the air and forest growth?" This question has been the subject of a great deal of discussion among able scientists, and we believe the balance of argument is in favor of the theory that there is a relationship existing between vegetation and the humidity of the air. The writer hopes he may have been successful in showing that a large proportion of the atmospheric vapor may be accounted for through the process of transpiration from plant life, that is, where there exists a fair percentage of woodland, say from twenty-five to thirty per cent.; so that now the above query may, we think, be answered in the affirmative. Under these circumstances the practice of forest culture as a means of improving atmospheric conditions, cannot be too highly commended.

MODES OF SPREADING AND MEANS OF EXTINGUISHING THE MAPLE-TREE BARK-LOUSE.

IN

BY EMILY A. SMITH.

N the October number of the AMERICAN NATURALIST I gave the life history of Lecanium acericorticis Fitch, and now conclude with the modes of spreading and the best artificial means of destroying the insect.

The disposition of the female to remain upon the same tree throughout its entire existence renders the modes of spreading from tree to tree incidental to outside influences. They are conveyed from one locality to another by the transportation of the trees while the females are upon the limbs, and are so nearly the color of the tree itself that without a magnifier are easily overlooked. The waxy mass exuded by the female in which she deposits her eggs, contains a sweet substance which is much sought after by various species of flies and wasps. When the young insect emerges from the egg, the tendency is to wander about for a time before settling upon the leaves, and the presence of the wasps and flies upon the tree in search of food at this time attracts the young lice and they attach themselves to their hairy legs and are thus conveyed to other trees. The wind and rain detach the egg-mass from the limb and convey it to other localities while the eggs are yet within.

The L. acericorticis are kept somewhat in subjection by the aid of the natural enemies and parasites found preying upon them; but when they increase beyond the power of these friends of ours to control them, artificial means must be resorted to.

The experience of the past summer differs from that formerly known in that the insects were found upon all parts of the tree instead of remaining upon the lower branches as was heretofore supposed. They are thus made more difficult to reach. When the lice are first hatched they are very small and delicate. A wash containing an alkaline solution applied at this time is sufficient to destroy them. I found that by attaching a wire bag to a common sprinkling hose, filling the bag with soft soap and turning on the water, a soap-suds was formed which would at once kill the insects; the scarcity of the water system in small cities renders this plan impracticable, and experiments led to one plan, easily attained by all, and which proved successful the past

season.

The plan recommended is as follows: Charge a fire extinguisher in the usual manner with bi-carbonate of soda and sulphuric acid; add to the water one spoonful of crude carbolic acid to every eight gallons of water. Apply this to the tree and the force from the extinguisher will convey the fluid to all parts of the tree alike; the disposition of the insects to settle upon the lower surface of the leaf and limb serve to further this plan. Two applications should be made upon the same tree; the first, three weeks after first deposition of eggs, and the second, four weeks from the first application. If the work is delayed the insects become strong and the strength of the solution must be increased, which would be liable to injure the tree itself. The actual cost is not exceeding twenty cents an application, which is trifling compared to the cost of replacing the tree. That the experiment may prove successful it is necessary to make the work thorough throughout a locality, since in a short time they return from the infested trees.

Examining the male L. acericorticis since my previous article, I find my doubts confirmed with reference to the non-existence of the two halters or balancers in the place of lower wings. After close examination with a high power and living specimens, I fail to find them, and conclude that in this species they do not exist, or if at all, in a rudimentary state.

M. V. Signoret states that when the male Lecanium is prepared to come out it lifts that membrane which rests slightly fixed by the head end. Observation with this species shows this is not reliable with all Lecania. When the male of this species is about to emerge from the larval scale, it backs out with the wings closely adhering to the body. The empty scales will, upon examination, be found closely attached to the leaf or limb at the head end, while at the opposite end it is loosened.

-:0:

RECENT LITERATURE.

MACALISTER'S ZOOLOGY OF THE VERTEBRATES.1- This little manual is chiefly concerned with the morphology of the classes and orders of vertebrate animals, with slight, condensed references to their habits, physiology and classification, but with no chapters treating of their zoo-geographical distribution, or geological suc

1 Zoology of the Vertebrate Animals. By ALEX. MACALISTER, M.D. Specially revised for American Students, by A S. PACKARD, JR., M.D. New York, Henry Holt & Co., 1878. 12mo, pp. 134, with 59 figures.