We see in the Porter scene in Macbeth a suspension of this nature; but Shakespeare used it sparingly, unless, indeed, we are to consider as a deliberate point of art the retardation of movement commonly observable in the fourth acts of his tragedies.

The dark appearance on the screen corresponding to the thinnest part of the film is probably due to refraction of the ray of light reflected from the second surface, consequent in its passing from a rare into a denser medium, and again from the denser medium into the rare, which refraction Lord Rayleigh considers to effect a retardation equivalent to half a wave length.

In the former case, by increasing the electrical force you overcome the resistance; while in the latter, by augmenting the electrical force you increase the retardation.

3. The effect of a different distribution of land and water in modifying the retardation caused by tidal friction, and of reducing it, under some circumstances, to a minimum, does not appear to be taken into account.

The fact appears to be that the amount of the resistance denominated friction depends, in a great measure, upon the nature of the unguent employed, and in certain cases the viscidity of the unguent may occasion a greater retardation than the resistance caused by the attrition.

The stations along the line were likely to cut in their relays when the test was in progress, and Bell's instruments were not arranged to overcome this retardation.

In October Faraday and I, at Lothbury, witnessed some remarkable experiments by Mr Latimer Clark on a galvanic current carried four times to and from Manchester by subterranean wires (more than 2000 miles) shewing the retardation of visible currents (at their maximum effect) and the concentration of active power.

It is the writer's art so to arrange words that they shall suffer the least possible retardation from the inevitable friction of the reader's mind.

[Footnote 20: It will be understood that I do not wish to deny that the earth's rotation may be undergoing retardation.]