8 REPORT — 1867. 



diudhj into the colour of the STtrrounding sea as in some previous months. 

 It showed as a distinct clear white spot, round which the sea was distinctly 

 of a deeper tint — one of the nondescript ochrcous browns. 'No symptoms of 

 a cloudy edge was visible vrith my 6| and power lOU." 



In contrast with this and as illustrative of Mr. Slack's opinion of varia- 

 tions in the appearance of Linne (see 2')ost, p. 22) I quote the following passage 

 from my note-book under date 1SG7, July 8 : — 



" The portion near the south border of the Mare Serenitatis was greatly in 

 contrast with Linne and its neighbourhood. While the most minute furrow 

 or cleft could have been seen near Sulpicius Gallus, linne was so indistinct that 

 nothing Avas visible except the spot of light, and this was quite undefined, so 

 that any Avell-marked margin, was invisible. Linne appeared as a light spot, 

 hriqliter towards the centre." 



On Oct. 17, to lo*", G. M. T., Mr. F. Bird, of Eirmingham, observed the 

 white spot but could not see the small crater, nor any trace whatever of sha- 

 dow, but he noticed that the place occupied by the small crater in July was 

 in October umisualhj bright. It is to be remarked that the state of the air 

 was almost as bad as possible at the time, so that it is doubtful if the small 

 crater was really replaced by the small bright spot. 



1867, Oct. 18, le"" to 20'' 30". Mi-. BrcKiNonAM observed the white spot 

 to be convex. 



Mr. Crossley on the same day saw the white spot as an irregular badly- 

 defined patch, especially towards Bessel, on which side near the centre was 

 the only shadow visible, which might have been the shadow of the supposed 

 central peak from its position. 



Analogous Spots. 



The spot which, so far as I am aware, exhibits the closest analogy to 

 Linne in its present state is lY A* ^\ IT A^^'' : sec Eeport, 1866, pp. 251, 

 262 and 276, where it is simply recorded as a bright spot. 1867, May 11, 

 8" 0" to S** 30™, I record : — IV A*'', TVA^^^ is a shallow crater on the 

 S.W. side of the ridge forming the X.E. boundary of Hipparchus. 1867, 

 Oct. 7, Rev. "\V. 0. "Williams of PwUheli recorded it as " veiy bright," but 

 said nothing of a crater. 



On Oct. 17, IS*" to 1.5'', G. M. T., Mr. Williams noticed it as a very con- 

 spicuous crater, and on Oct. 18, 17'' to 19'', G. M. T., it was also very con- 

 spicuous with a central cone casting a shadow. . In preparing area IV A^ 

 for engraving, I have met with a spot still more analogous to Linne. It is 

 west of Horrox, is marked IV A^^ ^"^ , and will be fully described in the letter- 

 press of IV A/3. 



Estimations and measures of the White Spot. 



Table I. contains estimations and measures of the extent of the white spot 

 in seconds of arc, English feet, and French metres. Those marked (*) are 

 measures, all at an angle of position=0°, except the measures by Mr. Huggins 

 marked respectively (t) the length, and {%) the breadth of the white spot. 

 The angles of position of these measures arc not given. As the same angle 

 of jiosition gives a different line of measurement on the moon's smrface from 

 day to day, the measures are not referable to the same line across the 

 white spot. 



The number of English feet subtending an angle of l"-0 at the centre of 

 the moon's disk at mean distance is 6116-7. At any given distance from the 

 centre this quantity is increased in the proportion of the secant of the angle. 



I 



