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.