90 
cool one-twelfth of a degree, or if a mass of air be heated to any excess 
above the surrounding mass it will fall to one-half of that excess in about 
one-twelfth of a second. 
For reasons stated in the preceding paper it is evident that this value 
must err rather in being too large than in being too small. 
PRELIMINARY Resutts By A New MerHop FoR THE Stupy OF IMPACT.* 
By A. W. Durr ann J. B. MEYER. 
The purpose of this paper is to briefly describe an apparatus for the study of 
impact of masses of wood on one another, and to state a few results obtained by 
means of it. It was intended to include in the investigation not only the change 
in the relative velocity of the impinging bodies produced by impact, but also the 
length of time the bodies are in contact, the closeness of approach produced by 
their mutual compression, and the internal vibrations to which impact gives 
rise. The apparatus was constructed by Mr. Meyer, and the present results 
obtained by him early in this year, but only a small part of the contemplated 
work was completed when it had to be discontinued. Calling, as usual, the ratio 
of the velocity of separation after impact to the velocity of approach before 
impact the coefficient of restitution, it may be stated that the results to be given 
here are only a few isolated determinations of the coefficient of restitution and 
of the time of contact. 
In principle the apparatus consists of a block dropped vertically on a much 
larger mass of the same material, the circumstances of the impact being recorded 
in a curve traced by a pencil attached to the block on a vertical revolving drum 
covered with a sheet of paper. To describe the apparatus more fully, it consists 
of two vertical beams mortised in a massive cross-shaped base, the beams adjust- 
able so that the space between can be regulated. The height of the beams is 8 
feet. Between these beams as guides the block can descend with comparatively 
little friction. On the base, the larger of the two impinging masses, or the plate 
as we shall eall it, is rigidly clamped. Immediately in front of the beams is fixed 
on cone bearings a vertical rotating cylinder around which a sheet of paper is 
wrapped. The cylinder is 2 feet in diameter and 2} feet in height. Fastened to 
the top of the descending block is a small removable board, to which is attached 
a brass tube carrying a pencil. The tube is secured in position by a catch attached 
*This paper is an abstract of a thesis presented by Mr. J.B. Meyer for the degree of 
B.Se., and placed in the library of Purdue University. 
