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losophy, ascribe the storm-producing air currents to magnetic forces of the earth, and the eddies and storms as a result of a readjustment of these forces.

And yet, while we may admit that the great storm movements are due to cosmic causes, we must not overlook that within their path there are minor terrestrial influences, sometimes not of entirely uncontrollable magnitude, which seem to influence within certain limits the localization of storms and the temporal distribution. We claim this influence for instance for forest areas, water surfaces, etc.

Altogether the theories for storm formation, while perhaps sufficient to explain the general philosophy, do not seem capable of explaining satisfactorily the smaller modifications and side shows, as we may call the exhibition of local showers, thunderstorms, and squalls. Nor can it be said that the detail of the manner in which the vapor condenses and the rain drop is formed, or in fact the forces active or conditions necessary in this condensation are fully known or understood. Who could, for instance, account for the fact that the dewpoint may be at and above 100 without precipitation occurring? We know some seemingly necessary conditions, but we do not know all. For want of experimental knowledge meteorology seems to have lagged behind the times.

While the mass movements that are calculated to satisfy the existing theories of general storm formation may be necessary for such formation, is it altogether inconceivable or unphilosophical to think that other, molecular, forces may participate and in fact be a condition sine qua non in forming precipitation? Is it not also conceivable that, as in many chemical reactions, it is only necessary to give the impetus to molecular motion, to initiate the change, metabolism, which, being induced at some center of formation, spreads and assumes greater and greater proportions, similar processes may take place in the condensation of vapor from the air? If such were the case the expectation of at least a partial control by human agency might well be realized. Suggestions of this kind have been made before, not only by those who would suggest any forces to explain phenomena without understanding the possibilities of such forces to do the work, but by physicists upon experimental basis.

Laboratory experiments by Mr. Aiton seem to indicate the presence of dust particles as an essential condition for rain production; and, although Professor Abbe “dismisses from consideration at present " the influence of atmospheric electricity in storm production, he does so only because we know too little about it, and because an assumption of such influence does not seem to help the accepted theories of air movements as sole causes. Even so, he is compelled to admit that "actual measurements of electrical potential would seem to show that two masses of air in extreme conditions may attract or repel each other electrically to an extent sufficient to produce appreciable phenomena of motion even in comparison with the far more important motions produced by solar heat and terrestrial gravity.”

That the air is generally negatively electric during rain storms was first established from over ten thousand observations by Herschel. Lord Rayleigh showed experimentally that moderately electrified water drops tend to coalesce, but that strongly electrified drops repel one another, from which we may infer a real causal connection between rain and electrical manifestations; and after all, even though the ascensional current may be the primary cause for cloud formation, electric conditions may determine the precipitation. We have hitherto been told that the electrical discharges during thunderstorms are the sequel and not the cause of the condensation; but this is by no means proved. Nor is the following explanation of any assumed effect, given by Professor Abbe, the only possible


Even if we allow that the condensation of smaller cloud particles into large rain drops and their consequent fall to the ground depends upon the electrical discharge, yet this assumption if adopted will merely modify our mechanical views somewhat, as follows: The latent heat evolved in condensation must be considered as not wholly consumed in directly warming the air, but as partially employed in maintaining a state of electrical disturbance or tension, which latter comes to an end as soon as the flash or the silent discharge of electricity occurs. At this moment, therefore, on the one hand larger drops are formed and fall to the ground, and on the other hand the energy that had been potentially present in the electric phenomena now becomes heat and warms and expands the air. Thus the electric tension and its concluding flash have merely served to delay the communication to the air of the heat that was a few minutes before present in the vapor.

It was Sir William Thompson who first suggested that changes of weather might be foretold by the change from positive to negative electricity of the air or the reverse, and who devised the instruments for such observations in the electrometer and “water dropper." Unfortunately when, some few years ago, the U. S. Signal Service undertook some experiments in that line, under the direction of Prof. T. C. Mendenhall, this object of weather prediction was kept in the foreground, and the experiments, which form the basis of a voluminous report still unpublished, were only too soon abandoned because they did not yield readily results for the purpose in view. I am assured by the gentleman who was in charge of these investigations that, if carried on without this immediate object in view, they would undoubtedly have led to a better understanding of atmospheric conditions, and are worthy of further pursuit.

In conclusion I may refer to the observation that dust particles are found always charged with positive electricity, which may account for their office in rain production, and that experiments by Professor Trowbridge, of Harvard, on the effect of flames upon the electric conditions of the air would lend countenance to the belief in the effect of fires on rainfall, while the possible origination of electric currents as a result of friction in cannonades is suggested by Mr. Powers as an explanation of their assumed effect.

We may say, then, that at this stage of meteorological knowledge we are not justified in expecting any results from trials as proposed for the production of artificial rainfall, and that it were better to increase this knowledge first by simple laboratory investigations and experiments preliminary to experiments on a larger scale.

If explosions are to be tried at once then it would be necessary at least to take all possible precautions to ascertain the state of the atmosphere in all particulars before, during, and after the explosions, and to conduct and refer to the experiments rather as investigations into the effect of explosions upon the atmosphere than with the ultimate desired result in the foreground.


The same recommendations which have been repeatedly made in my former reports as to the work to be pursued by the Division and as to the manner of advancing the forestry interests of the country in general may be repeated, only with more emphasis than before, although with the increased appropriations and facilities provided this year, not only can certain lines of work, which the Division had tentatively laid out, be placed upon a desirable basis, but it will also be possible to devote more time and attention to the missionary work, which must needs still form part of our endeavor to change the forest policy of the United States.


Chief of Division of Forestry. Hon. J. M. RUSK,




SIR: I have the honor to present herewith my annual report as Entomologist for the calendar year 1890.

À summary of the work of the Division for the year has been presented in your annual report to the President, and is reprinted in the opening pages of this volume. The subject, therefore, needs no elaboration here. The articles which follow are short and condensed accounts of some of the more interesting observations and experiments of the year.

That upon the boll worm investigation is merely a report of progress and a discussion of plans. The army worm has made two destructive appearances during the year, one in Maryland and the other in Indiana, and as these appearances have an interesting bearing upon the subject of influence of climate I have devoted some little space to their consideration. Following this article I have brought together some notes upon the bronzy cut-worm, an insect which is often taken for the army worm, and the consideration of which is additionally appropriate at this time for the reason that it is commonly affected with a bacterial disease which may possibly be transmitted to the boll worm. Some observations and remedial experiments upon the horn fly of cattle are brought together as supplementary to the details in my last annual report. Four new species of the genus Icerya, recently described in INSECT LIFE, are referred to, because of their close relation to the fluted scale of California, and of the economic interest attaching to the species of the genus. Considerable work has been done in California during the past year upon the question of remedies for the scale-insects other than the fluted scale. The results of these experiments upon the so-called black scale (Lecanium olece) are given in this report and some interesting experiments upon the red scale (Aonidia aurantii) are mentioned in the summary of the reports of agents. Concerning this species two distinct forms have long since been known and these are considered in detail and their differences set forth. The greenstriped maple-worm is an insect which has been frequently brought to the attention of the Division of late years, and in order to make its life history and the remedies against it more generally known, I have included a short account. The rose chafer (Macrodactylus subspinosus) has also been very prominent of late and is also treated herewith. Another insect which may possibly soon gain economic importance in this country is considered in the article headed “A New Peach Worm,” while the work of the field agents of the Division during the season is summarized in a concluding article, the full text of their reports being reserved for a bulletin.

It were premature to refer in detail to a number of minor investigations which are in progress, but I may mention the fact that I have made during the year an attempt towards repaying the people of Australia and New Zealand in some degree for their assistance in the introduction of Vedalia cardinalis into California, by sending them predaceous and parasitic species which may help to reduce the numbers of the codling moth, an insect which is, perhaps, more destructive in those countries than in any other part of the world. Among the insect enemies of the codling moth recently discovered by Mr. Koebele, in California, is a Neuropteron of the genus Raphidia, the larva of which is very active and rapacious and feeds extensively upon the apple worm after these have issued from the apples. A shipment consigned to Mr. R. Allan Wight, of Auckland, arrived in fairly good condition, seventeen being alive, sixteen in the pupa state, and one in the larva state. The latter fed voraciously upon the first apple worms which were offered to it. The latest advices are somewhat discouraging, as there is no certainty that the insect has survived and been colonized there. I have also made efforts to introduce some of the European parasites of the Hessian fly which do not yet occur in the United States.

That these efforts have not been successful is largely due to the fact that they had to be made through correspondence. The clause restricting travel to the United States is still maintained in the appropriations for the Division, and this seems very strange in face of the example of Vedalia, the successful importation of which has been worth many millions of dollars to the people of California, but which could not well have been made without sending an agent to Australia. I again urgently recommend that steps be taken to have this unnecessary restriction removed.

An interesting event of the year is the appearance of the hop fly (Phorodon humuli) upon the Pacific coast. This insect has up to the present season been known to occur only in Europe and in the hop fields of the United States east of the Mississippi river.

The correspondence of the Division has been rather larger than last year and about three thousand eight hundred letters have been written to correspondents in answer to inquiries and a large number of others have been answered by circular. The collections have been greatly added to by donations, purchases, and exchanges, and the amount of Museum work in the way of the determination of species, not only for investigators in all parts of the country, but for the agents of the Division and the entomologists of experiment stations, has greatly increased. As stated in my last report, this branch of the work of the Division is growing more and more onerous, and while it is extremely important, its results are shown in the reports published by those thus assisted rather than in any visible output of the Division.

The report has been kept within the limit as to length allotted to the Division. I greatly miss the opportunity of publishing extended articles upon important insects afforded in previous annual reports, but which present exigencies forbid. The insufficiency of the printing appropriation at the disposal of the Department will also not permit of the publication of as many or as long bulletins of the

regular series of the Division, or of special reports, as the accumulation of information in the Division demands.

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