In the first unit of time, the impacts are 2, 6, h, 2; and in the second 6, 2, h, 6.
Applying this notion to benzene, let us consider the impacts made by the carbon atom (I) which we will assume to be doubly linked to the carbon atom (2) and singly linked to (6), h standing for the hydrogen atom.
If it is the average distance irrespective of length of path and of number of impacts we should be justified in ascribing the effect to density, but if it is the number of impacts it would be more reasonable to ascribe it to pressure.
Experiments which will be discussed in § to seem to show that there is a difference in this respect between the impacts of similar and those of dissimilar molecules.
Of the six great impacts made upon the Confederacy, four were upon Virginian soil: the first Manassas campaign (1861), the Peninsular battles (1862), second Manassas (1862), Fredericksburg, Chancellorsville (1862-63) and the great Wilderness-Petersburg series of attacks (1864-65).
The cylinder is of volume u dt dS, so that the product of this and expression (9) must give the number of impacts between the area dS and molecules of the kind under consideration within the interval dt.
The homogeneity of vibration may also be diminished by molecular impacts, but the number of shocks in a given time depends on pressure and we may therefore expect to diminish the width of a line by diminishing the pressure.