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t of sciences。 But let me explain my meaning； without further eulogies on this beneficent Element。
If Fog were non…existent； all lines would appear equally and indistinguishably clear； and this is actually the case in those unhappy countries in which the atmosphere is perfectly dry and transparent。 But wherever there is a rich supply of Fog objects that are at a distance； say of three feet； are appreciably dimmer than those at a distance of two feet eleven inches； and the result is that by careful and constant experimental observation of comparative dimness and clearness； we are enabled to infer with great exactness the configuration of the object observed。
An instance will do more than a volume of generalities to make my meaning clear。
Suppose I see two individuals approaching whose rank I wish to ascertain。 They are； we will suppose； a Merchant and a Physician； or in other words； an Equilateral Triangle and a Pentagon： how am I to distinguish them？
C （1） ｜ … _ D ｜ ｜｜… _ ｜ ｜｜ … _ ｜ ｜｜ …＋（》 Eye…glance ___C' （2） ｜ / A｜｜ _ … ___… … _D' ｜ / ｜｜_ … __… ｜｜ … _ ｜/ _ … E ｜ ｜｜ … _ B ｜ ｜｜ … _ ｜ Eye…glance ｜｜ … _ ｜