beyond the capacity of the human mind to form anything near a true conception as to its shape or form.

A theory which has been long expounded by certain scientists in regards to the lightning discharge is that it is of an oscillatory nature. This theory is founded on the fact that when two bodies are electrically charged to opposite sines and brought within certain proximity of each other, they tend to neutralize each other, that is, electricity will flow from one body to the other until there is no difference of potential between them. If the difference of potential or electrical pressure between the two bodies is not very great, the flow of electricity will be gradual, but if the pressure becomes excessive the

electricity will jump from the body of the higher potential to that of the lower, tending to raise the potential of the one and lower that of the other. Owing to the suddenness of this discharge and the fact that electricity acts as though it possessed inertia, the flow will not stop when equilibrium is reached.

The body into which the electricity is flowing will be raised to a higher potential than that from which it is flowing, so there will be a reversal of the flow back to the first body. This back and forth flow of electricity will continue with decreasing value until the potential of the two bodies becomes equal. This is what is called the oscillation of the discharge and can be compared to the swing of a pendulum, each swing becoming less than the one preceding until the pendulum comes to rest, only in the case of electrical discharge, the oscillations are extremely rapid, running up into the hundreds of thousands per second.

In the case of the lightning discharge the clouds represent one body and a small area of the earth the other body.

A difference of potential or electrical pressure is generated between the cloud and earth by the motion of the cloud and other causes. This pressure soon reaches an enormous value and eventually breaks through the intervening air between cloud and earth. It is through this rupture of the air that the electricity flows which tends to neutralize the potential of the cloud and earth, and this is what we know as the lightning flash.

Although it has been conclusively proven in the laboratory that small electrical discharges are oscillatory in nature, for it is on this principle that the

wonderful wireless telegraph is worked, nevertheless some scientists hold that it is doubtful whether lightning discharges are very oscillatory owing to the very high resistance which must be encountered in a long lightning flash, it being held that this resistance in a flash of a mile or more in length is enough to dampen out the oscillations of the most severe discharge.

Photography is playing a prominent part in helping to prove or disprove this theory of lightning oscillation. The camera has demonstrated that lightning discharges are frequently discontinuous, that is, the discharge is not one flash as it is seen by the eye, but is composed of several distinct and separate discharges. The theory of this is that after the first discharge makes a path through the air for the flow of electricity between the cloud and earth, the cloud again charges up before this air path has closed off so that another discharge will take place at a much lower potential. Sometimes several of these discharges will take place before the air path is broken.

The photographs which demonstrate this phenomenon are produced by revolving a camera at a uniform rate of speed with opened lens during the lightning discharges. Some very fine photographs of lightning taken with a moving camera have been made by Mr. Alex. Larsen, and can be seen in the "Annual Report of the Smithsonian Institution," for the year 1905.

One of the photographs shows as many as forty separate discharges, and Mr. Larsen estimates the duration of this flash as .624 second.

The photographs accompanying this article were made by the writer dur

ing the early spring of 1908, being taken near Pittsburg, Pa., in the month of April, during one of the first thunder storms of the season.

The object is to show the flashes as they appeared to the eye and as they really were. This was done by using two cameras, one stationary and one revolving.

Photographs No. 1 and 2 are of the same discharge. No. I was taken with a stationary camera, showing how the flash appeared to the eye; No. 2 was taken with a revolving camera, and shows that this flash was composed of about 36 separate discharges. The camera was mounted on a vertical axis and rotated at about 12 revolutions per minute, the lens having an unobstructed view of all parts of the sky.

The highlight spots on photograph No. 2 are probably due to the fact that some brush discharges, or what is popularly known as "heat lightning," were taking place in the sky opposite to where the heavier discharges were taking place. These brush discharges were almost continuous, and could have been prevented from affecting the plate by shielding the lens when it was pointed toward that part of the sky.

Photographs No. 3 and 4 show another flash as it appeared to the eye and as it really was. This flash was apparently composed of about 38 separate discharges.

Photographs No. 5 and 6 are of the same flash, No. 5 being taken with the stationary camera and No. 6 with the moving camera, and is composed of about 40 separate discharges.

Most all amateurs have the means at hand to obtain results as shown here. It is not necessary that the camera be mounted and revolved unless accurate measurements of time are to be made. It can be held in the hand and swung from side to side, keeping the lens pointed toward the sky where the discharges are taking place.

It is hoped by the writer that this article will interest some of the readers of THE PHOTOGRAPHIC TIMES in this fascinating branch of photography, so that, during the coming summer, they may derive some additional pleasure from their cameras and possibly furnish some valuable data for the cause of science.

PHOTOGRAPHIC JOTTINGS.

F. C. LAMBERT, M.A., F.R.P.S.

P

HOTOGRAPHERS never seem weary of talking about development, therefore I may be pardoned if I add a word or two on this topic. in connection with some experiments I have had in hand recently. These were prompted by a querist asking for a developer of the M. Q. type but made up without metol, as that agent developed sores on his fingers. To skip right away to the end of the story the essence of the matter is as follows: Take 2 ounces of soda sulphite (crystals), 2 ounces of soda carbonate (crystals), 1⁄2 ounce soda (or potash) metabisulphite, and add water to make a total bulk of 10 fluid ounces. When the solids are dissolved divide the 10 ounces into two equal parts,

viz., A and B. Now to A. add 30 grains Eikonogen, to B add 30 grains Quinol (Hydrokinone). We now have two stock solutions which will keep fairly well for some time. To use them we may take I ounce A and add 1 ounce of water, or we may take 1 ounce B and add 1 ounce water, or we may take 1 ounce A, 1 ounce B, and add 2 ounces water.

By using the dilute A alone we have a developer that gives good shadow detail with delicacy of gradation rather than vigorous contrasts unless the development be very prolonged. In fact A is just what we want for soft contrast effects such for instance as home portraiture, interiors, and brilliantly lit landscapes that have had a minimum exposure, and, generally speaking, this is the kind of negative one aims at when an enlarged result is the ultimate goal.

On the other hand B is the thing to use when strong contrasts are aimed at, as for example when trying to get the brightest effects we can when the lighting is dull and poor. Then again, when copying we want good bright sparkling negatives. Or yet again after focusing with a large stop we forget to change the stop but imagine we have done so and then give an exposure on the small stop basis; then on capping the lens the inspiration flashes on the mind, "I forgot to change the stop." The result is perhaps a ten times overexposure. In such a case add at least one grain of bromide to dilute B and hope for the best. Dilute B is also quite good for bright lantern-slide effects. But the foregoing are what we may call the special cases, while for the usual run of things we want an average quality developer, and this I fancy we get by blending equal parts of A and B with an equal bulk of water. If the exposures have been reasonably correct I do not think one need trouble about any bromide at all with plates that have an average present-day character for clean