This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1886 Excerpt: ...a plan of the markings on the floor of Plato, in which the position of most of the light spots are indicated with a considerable degree of accuracy. Of the remaining new spots, No. 44 lies just east of 22, 46 north-west of 17, 51 just west of 41, 52 east of 14,53 south-east of 6, 54 east of 39, and 55 just east of 13. All these spots form close pairs, or double spots, with those spots contiguous to which they lie. In fact, the tendency of the spots, in Plato as elsewhere, to collect in pairs and groups is a significant circumstance which must not be forgotten when considering the origin and nature of these interesting little objects. In the beginning of the Second Period a new method of observation was adopted, which, increasing greatly as it does the accuracy of the results, may be recommended for adoption in similar cases. The brightness, or plainness, of the spots is registered according to a recognized and definite scale, in which spot No. 1, at its usual plainness at about the time of full Moon (at which time its brightness remains substantially constant), is assumed as the standard. The effect of this refinement in the method of observation is to nearly double the numbers available for calculating the mean visibilities, whilst it is not going too far to affirm that the accuracy of the results is quadrupled. The adoption of some method of this kind becomes absolutely essential in cases where the observations are extended over periods of many years; for where, as with the old method, the spots seen at each observation of Plato are merely recorded, after two or three years the observers become well acquainted with the appearance and situation of the different markings, and it will happen that a large number of spots will be recorded on nearly every night...
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