WEATHER conditions during the month of November have shown only too clearly the paralysing effect on motor transport of a heavy fog, and the observant driver is bound to have questioned whether some method could not be devised to enable him to make steady progress, even if only at reduced speed. In thick fog, of course, it is useless to keep the head-lights on, for the glare which is reflected back by the bank of vapour dazzles the driver and counteracts any extra penetrating effect which the powerful lights might give. Fog lights which project a beam diagonally downwards are quite effective, but the modern high radiator often conceals the patch of road which the fog lamps reveal, and orange-tinted lenses, which are also extensively used, in some cases seem to be beneficial, but most of them do little but reduce the intensity of the light projected, without overcoming the reflection problem. What most motorists want is to utilise the normal light of the headlights, thus obtaining a fairly long forward beam, so that they may have warning of obstacles before the car is upon

them, and the problem has been tackled in this way by the makers of the Nebulite lenses.

As is well-known, what we call white light is made up of a number of rays of different wave-lengths and colours, varying from the red and orange rays, which are of long wave-length, to the short blue and violet. Fog consists of minute globules of water-vapour, which reflect short wave-length light, but between which the long wave-lengths are able to pass. The problem therefore resolves itself into producing a filter which will suppress the light of short wave-length while allowing the long orange and red rays to pass, and after much research by means of the spectroscope this object has been attained. The Nebulite lenses, which are made by the well-known glass manufacturers, Messrs. Pilkington Bros., are tinted according to the formula which was discovered, and as they can be had in any size, and simply replace the normal lamp glasses, may be fitted with a minimum of trouble. Special orange-coloured discs are also supplied free of charge to prevent dazzle from the side-lamps.

In foggy weather it is found that the head-lamps can be kept in the " full-on " position without any disagreeable backreflections, and the penetrating effect of the beams is limited only by the actual density of the vapour and the candlepower of the lamps fitted. Under normal conditions the light-beam has a pale yellow appearance, and suffers a slight reduction of all-out range, which is compensated for by the fact that dark objects are thrown up into greater relief than with the ordinary white beams. Cars meeting the oncoming lights seem to find them less dazzling than that of the normal head-lamp, and the-greenish light is definitely restful to drive behind. Nebulitelenses, incidentally, were used with success by Healey and other well-known drivers in the Monte Carlo and R.A.C. Rallies this year.

The lenses may be obtained from the Nebulite Retail Company, 60, Strand, London, W.C. 2, and vary in price from 15s. for those under 6 inches in diameter, to 28s. for the 11 inch size. The only particulars required are the make and diameter of the lamps.