. Biographies of distinguished scientific men. Scientists. DIFFERENCES OF ROUTE. 207 we operate with white hght in phenomena of colora- tion. In the course of such singular results we may, perhaps, be curious to find the numerical value of these differences of route, so often mentioned, and which place two rays in the conditions either of accordance or com- plete destruction. I will mention, then, that for red light we pass from the one of these conditions to the other w^hen we make the difference of route amount to three ten thousandths of a millimetre.* * The numerical values of the differen
. Biographies of distinguished scientific men. Scientists. DIFFERENCES OF ROUTE. 207 we operate with white hght in phenomena of colora- tion. In the course of such singular results we may, perhaps, be curious to find the numerical value of these differences of route, so often mentioned, and which place two rays in the conditions either of accordance or com- plete destruction. I will mention, then, that for red light we pass from the one of these conditions to the other w^hen we make the difference of route amount to three ten thousandths of a millimetre.* * The numerical values of the differences of route, as Arago ex- presses it, or the connection of the wave lengths for different rays with the intervals between the stripes is easily investigated; and the latter being readily susceptible of accurate micrometrical measure- ment, the former may be deduced. Let two rays be inclined at a very small angle 2 6. Then the crossings of the waves will give rise to a set of bright and dark points at -)-, o, &c., according as like or unlike portions meet. Let c be the interval between two successive bright points and Z the wave lengths. Then we have obviously the rela- tion — c = - cot d. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Arago, F. (François), 1786-1853; Smyth, W. H. (William Henry), 1788-1865; Powell, Baden, 1796-1860; Grant, Robert, 1814-1892; Fairbairn, William, Sir, 1789-1874. Boston, Ticknor and Fields
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