Progress in Science.

New Zealand Graphic, Volume XLVII, Issue 8, 21 February 1912, Page 42

Progress in Science.

POWERFUL ELECTROMAGNET FOR OCULISTS.

THE electromagnet designed for the use of oculists by Dr. Haab, director of the Zurich eye elinie,

and shown in the accompanying photograph, is the most powerful and efficient apparatus of this kind in existence. According to Dr. Haab, the principal requirements of such an instrument are the following: 1. The magnet must be capable of developing very great tractive force. 2. It must be placed horizontally, and its circuit must be made and broken by the operation of a pedal. 3. The working pole must have a form adapted to its peculiar function and its dimensions must bear the proper relation to those of the coil.

The first condition is very important. The small electromagnets which are commonly used by oculists often fail at the critical moment, owing to their lack of adequate magnetic strength, and thus endanger the success of the operation. The method of making and breaking the circuit by the foot of the operator possesses great advantages, because it

leaves both hands free for the control of the eye and body of the patient, and makes it unnecessary to remove the magnet in order to stop its action. This last point is exceedingly important for, even with the most perfect suspension, it would be impossible to withdraw the heavy electromagnet from the eye quickly enough to prevent the iron filing or other foreign substance from being drawn into a region where its presence is not desired. When the circuit is opened and closed by a pedal 'the magnet need not be suspended.

Dr. Haab regards the suspension method not only as impracticable for the heavy magnets which he employs, but as incorrect in principle. His experience proves that it suffices to support the magnet in such a manner that its axis can be turned to any direction in a horizontal plane.

In regard to the form of the working pole, it is obvious that its action wifi be weakened in proportion to the extent to which it protrudes from the coil. It must not, however, be so short that the coil interferes with the view’ of the field of operation, as is the case in some of the newer large electromagnets.

The magnet is of the bell form. The working pole is a cone of 90 degrees, and this end of the coil is tapered sufficiently to give the operator a clear view of the field up to the tip of the magnet pole. Four pointed tips accompany each apparatus.

The idle pole is expanded into the form of a bell which covers and protects the greater - part of the coil. This construction possesses the additional advantage of restricting the escape of lines of force to one side and diminishing the area of the external magnetic field. The magnet, is mounted on a east iron pillar, in such a manner that it can easily turned in ary direction. A special device protects the contacts from injurious sparking. The currentdensity in the coil is very small in comparison with its density in other electromagnets. Hence very little heat is developed—a condition essential to permanent efficiency. In tractive power Haab’s electromagnet stands at the head of all known electromagnets used by oculists. At a distance of 1.2 inches, for example, it exerts a pull more than twice as strong as that of the largest Volkmann magnet. The electromagnet is designed for use on direct current circuits of CO to 300 volts, but it can be employed on alternating uniphase or triphase circuits, with the aid of a suitable transformer. The maximum power required is about one kilowatt. The total weight of the apparatus is about 286 pounds. This apparatus, although designed primarily for the use of oculists, is admirably well adapted for the extraction of iron filings and splinters, hammerscale, etc., from wounds in any part of the body. Hence it may advantageously be installed in the hospital rooms of all large mining and metallurgical estab-

lishments. Experience shows that th< magnets now employed in these room* are used as often on hands and arms as on eyes. Wounds incurred in planing iron are as often flleed with fine splintery of iron. The removal of these splinters singly with pincers or needles is a tedious and painful operation, but all of the iron or steel particles can be extracted quickly by means of a powerful magnet.

tlectrtc Culture.

Electric culture was the subject of St recent demonstration and lecture at the! Royal Botanic Gardens, where experiments have been inaugurated and will be carried still further. The effect of electric culture on old wheat of which not more than 30 per cent, had 'been expected to germinate was remarkable, for on being turned out of the pot in which it had been sown three weeks ago, it was demonstrated to the audience that every seed had proved productive. In order to show the rapid germination of wheat under electric treatment, a layer of soil was placed on a positive plate, sprinkled with grain, and covered by the negative plate, and a continuous current of 80 volts, changed later to an alternating current of 10,000 volts, was applied. After about twenty minutes the seeds were examined and microscopic indications of growth were quite apparent to the accustomed eye. The forcing of the plant-food combined with insecticide into a tree or plant by the electric machine was exemplified in a rubber tree which was treated three weeks before, and had since put on some new leaves, while its yield on tapping was stated to have increased. The insecticide and food were introduced with water through the roots, the natural pumping-power of the tree being stimulated by the current, applied low down on the stem. As to the effect on soil, the lecturer said that, charged with the special chemical food and treated with the electric current, a field would be cleared of insects and w’ell supplied with nitrogen. This could be done at a trifling expense, but the apparatus would cost £6OO. The invention was distinct from other methods, combining varied currents with chemical treatment. It was particularly applicable to the acceleration of the germination o£ seed and to the regeneration and revitalising of übuat life.