Page images
PDF
EPUB

The latter swings to one side, completes the relay circuit at b, thus operating the solenoid L and (by reason of the cord) breaking the R solenoid circuit. In consequence the pointer (oscillating through one division of the dial) indicates directly the "minimum E.M.F. for electrolysis."

TO MEASURE TIME.

With the sign block "Hundredth minutes" (17, 23; 20, 24) in position, the instrument acts as a stop watch. The pointer is set in motion when contact is made between the terminals, and stops immediately the contact is broken. The speed of the motor can be adjusted

[blocks in formation]

(rheostat and speed indicator) so that the pointer moves over the dial from 0 to 100 in one minute.

The momentum of the fly wheel is so great, and the friction of the resistance wheel (W) on its bearings so slight, that no appreciable difference in rate is caused by bringing the solenoid into operation.

TO MEASURE TEMPERATURE.

As the electrical resistance of copper is a linear function of the temperature, it is only necessary to express the resistance of a coil of copper wire in suitable units in order to have its temperature in degrees centigrade.

This may be effected by connecting in series with the wheel a stationary coil, the resistance of which (about 500 ohms) depends on the temperature coefficient of the wire employed as a thermometer.

[blocks in formation]

I. Some Recent Work in Economic Entomology.

By REV. C. J. S. BETHUNE, M.A., D.C.L.

(Read May 29, 1900.)

In accordance with the regulations of this society the duty devolves upon me, as President of Section IV. during the present session, of giving you "an address having reference to the special objects of the section." As we include within our objects the "Geological and Biological Sciences," it would be an impossible task for any one, in these days of necessary specialization, to cover the whole field or to attempt to give an account of all that is being accomplished in such extensive departments of science. Happily this difficulty is overcome by the system that prevails of electing from year to year to the Presidential chair a member who is devoted to some particular branch of study in relation to organized beings, whether animal or plant, whether living now upon the earth or belonging to some era in the far distant past. By this method each in turn has his opportunity of relating the progress that is being made in his own special department of investigation, announcing any discoveries of importance and setting forth any noteworthy additions to the sum of human knowledge.

Five years ago our colleague, Dr. James Fletcher, presented us with a short history of the progress of practical entomology, the subject in which I am more particularly interested, and two years ago I had the honour of reading before this section a paper on "The Rise and Progress of Entomology in Canada," there remains, therefore, but a short period for me to cover to-day and but few matters of particular interest to which attention may be drawn.

THE SAN JOSE SCALE (ASPIDIOTUS PERNICIOSUS, COMSTK.)

No insect attack of recent years in this country can be compared in importance with that of the San José Scale, and to no insect probably has public attention been more generally drawn. It is now a matter of common knowledge that the insect was first noticed as destructive in the San José Valley, California, in 1873, whence it has received its popular name, but from what part of the world it was brought to America is still a matter of conjecture and a subject of controversy; some contend that it came from Japan, others consider that the evidence points to South America, others again to Australia or New Zealand. The question might

seem of little practical importance now that the scale is fully established on this continent, but its solution may be of the highest value, inasmuch as it is evidently no serious pest where it came from and must therefore be kept in check by its natural enemies, which, as so often happens, have not accompanied it in its voyage to North America. If its native home could be discovered with certainty there would probably be no insuperable difficulty in importing the useful insect, or the vegetable parasite, as the case may be, which keeps it under control.

In 1880, it was scientifically described by Prof. Comstock under the name of Aspidiotus perniciosus, the specific designation proving to be most appropriate, though at that time and for many years longer its devastating work was confined to California. It was not until August, 1893, that it was noticed east of the Rocky Mountains; it was then found. to be injurious in an orchard in Virginia and was traced from there to some nursery gardens in New Jersey, whose managers had imported plum trees from California and distributed them, after a few years further growth in their plantations, far and wide throughout the Eastern States. In 1894, and again two years later, the scale was discovered in British Columbia, but on both occasions the affected trees were promptly destroyed and the infestation was put an end to. Only three years ago it was found for the first time in this province of Ontario in the counties of Kent and Lincoln where it soon revealed its destructive powers. Since that time it has continued to be a subject of absorbing interest among fruit growers and has led to the adoption of very stringent measures for its repression by both the Dominion and Provincial Legislatures. In the winter following its discovery in Canada, an Act was passed (January 17th, 1898) by the Legislature of Ontario forbidding the importation. or sale of any plants infested by the scale and providing for the inspection of orchards and the destruction by burning of all trees or plants found to be attacked. The Dominion Parliament almost immediately afterwards passed an Act (March 18th, 1898) which prohibited the importation into any part of the Dominion of any "nursery stock" from the United States, Australia, Japan and the Hawaiian Islands; greenhouse plants with the exception of roses, herbaceous perennials and bedding plants, all conifers, and bulbs and tubers, being free from liability to attack by the scale, were exempted by Order-in-Council from the operations of the Act.

Legislative enactments were also passed about the same time by no less than sixteen of the United States dealing more or less rigidly with the importation or distribution of infested plants and those liable to attack, and the destruction of those found to be affected. In Germany a decree was proclaimed (February 5th, 1898) absolutely prohibiting the

« PreviousContinue »