184 Transactions.— Miscellaneous. 
that the mere work of shearing the bodies when they come into impact, is 
such an excessively small fraction of the total energy, in cases of large 
masses, that it may be absolutely disregarded. As the whole of this 
reasoning holds good for all cases of the collision of approximately equal 
large bodies, it becomes evident therefore that these collisions are partial. 
There is, however, one exception, that where the larger body extends so 
as to include the smaller body completely in its path. The impact in this 
case is complete as regards the small body, and tangential on the larger, 
and although tending to produce rotation possesses none of the definite pro- 
perties of partial impact. It is clear that collisions may vary from the 
mere graze of the atmosphere of the two bodies, through the stage of cutting 
off a considerable ratio, up to the extreme case of complete impact, all of 
which possibilities tend to vary the result. Again, the two bodies may be 
intensely hot, or one hot and one cold; either or both may be solid, liquid, 
or gaseous, or mixtures of these physical conditions. They may have an 
original rotation of their own, and may have smaller bodies revolving around 
them. They may have had very different original proper motions, and may 
be of considerably different mass. Any of these peculiarities tends to alter 
the result attained at and after impact. Still, on the other hand, there are 
many broad well-marked generalizations which are sufficiently characteristic 
to mark out these partial collisions as a clearly defined genus, the phe- 
nomena resulting from them being easily recognizable to a skilled observer. 
The accompanying diagrams probably represent with some degree of 
accuracy the stages of a medium case of partial collision. I have attempted 
to draw these diagrams from independent reasoning on dynamical principles, 
and have consulted others ds to the accuracy of the reasoning. I must 
acknowledge my indebtedness for several valuable hints from Mr. N. K. 
Cherrill. The first figure (Pl. VI.) shows two bodies coming into impact—it 
will be seen that the bodies are distorted to an egg shape. The idea of this 
distortion was first suggested to me by Mr. Beverly, of Dunedin, who has 
been studying the various mathematical problems of complete cosmical 
impact for more thanadozen years. It will ultimately be found, when this 
question is discussed in detail, that this distortion produces some very 
interesting phenomena. The two following figures show the process of 
impact, and it is perfectly evident, from the mode of impact, the rare out- 
side of each body meeting with the denser inside of the other, that the two 
sides of the coalesced mass have a great deal of unbalanced momentum, 
acting in different directions, and tending to spin the mass on its centre. 
It is generic of partial impact that it must produce rotation. It will also be 
seen that this same residual motion, and the attraction of the retreating 
masses, tend to draw the mass into a spindle shape. It is also evident, all 
