Piece Of Cardboard Research Articles

Photographic Irradiation

As the question of whether irradiation is due to the imperfection of the instruments, or to an action taking place within the thickness of the collodion film, is a matter of considerable importance in all cases in which photography is made use of for the purposes of accurate measurement, I have repeated and somewhat varied the experiments which have lately been described in NATURE, vol. x. pp. 205, 223, by Mr. Ranyard. I therefore laid on a uranium dry plate a piece of platinum foil, and with full aperture of lens took, with an exposure of twenty-five minutes, a photograph of a piece of cardboard, in which were four parallel slits, hung against a background of bright sky. In spite of the long exposure, the images of the slits are sharply cut off at the place occupied by the edge of the platinum foil, though at the same time there are very marked traces of the outer hazy irradiation arising from reflection from the back of the plate. I then took with the same exposure, and under what seemed to be similar conditions of illumination, a photograph of the same cardboard sheet, on an extra-sensitive Liverpool plate, and again found that the images of the slits were sharply cut off. This seems to me to decisively show that the irradiation cannot be due to a spreading within the film, caused by the light dispersed from the highly illuminated particles in the collodion, as suggested by Mr. Aitken; and I feel inclined to agree with Lord Lindsay and Mr. Ranyard that it must be due to some cause that has its seat of action in front of the collodion film.

Simple Method of Studying Wave Motion

IT is difficult for a student to obtain a clear idea of the movement of the particles of a liquid or gas propagating a wave. To assist him models have been devised, but as a rule they are expensive and complicated. The following plan, based on the principle of the stroboscope, I have found extremely convenient. Take a piece of cardboard about 3 ft. long and 18 in. broad. Put this into the tin drum of a “zoetrope,” pressing the card well against the interior of the drum, so that it stands up forming a cardboard cylinder. With a lead pencil mark where the inside fold of card comes, and you have the right size of the cardboard to form the cylinder. Divide now the length of the cardboard into 12 equal strips. On each strip paint dots representing the wave you want to study, taking care that each wave is represented 1/12 behind its predecessor. Lastly, cut out 12 slits, about 8 in. by 1/4; in., between each representation of the wave; restore the card to the drum of the zoetrope, and then turning the cylinder and observing through the slits, the wave is seen, as the cylinder revolves, to advance with its characteristic motion, while by stopping out all but one of the particles represented the exact character of its oscillation, whether circular, elliptical, or linear, is clearly seen.

On approach caused by vibration

1. The chain of experiments which I have to describe arose from the endeavour to explain an observation that a delicately suspended piece of cardboard moves, from a considerable distance, towards a vibrating tuning fork. It will be preferable to detail the experiments, not in the order in which they occurred to me and were actually performed, but in the order in which I conceive them to form a logical sequence.

Proof of Napier's Rules

SUCH a structure in cardboard as that described by Prof. A, S. Herschel in NATURE, No. 106, may be found very useful in facilitating the study of the proof of “Napier's Rules,” but the ingenious learner might object that the demonstration was confined to one particular species of triangle—the isosceles right-angled with a perimeter equal to a quadrant; for Mr. Herschel's angles a and b are plainly equal, and together with c make up a right angle. The corresponding construction for any case would be as follow:—Take a circular piece of cardboard with centre D (referring to Mr. Herschel's diagram), and on the circumference, in the same direction, take any two arcs B1, 12. Let a perpendicular from B or D1 meet it in D, and a second from C or D2 meet it in A, and be produced to reach the circumference in B′. Finally, a semicircle on A B' as diameter and another with centre A and radius A C will determine by their intersection the.point C'. To a construction thus generalised all that Prof. Herschel adds would apply.

VII. On approach caused by vibration

The author observes that when a vibrating tuning-fork is held near to-a piece of cardboard, the latter has a tendency to approach the fork. Starting from this experiment, a series of experiments is described having for their object the determination of the cause and conditions of the fundamental observed fact.