42 REPORT—1868. 
supervenes ; but if the surface itself should at any time be altered so that 
with the same incidence of the sun’s rays the former altered appearance 
should be no longer observed, the change, of whatever nature it may be, 
could not in that case be referred to a purely optical source, some real 
change, either of a temporary or lasting character, must have transpired. 
While the change about to be described is constant for constant solar alti- 
tudes and azimuths, the question whether it is purely optical, or whether it 
is connected with a temporary but real diurnal change cannot be resolved ; 
but as soon as the character of the surface, as seen at sunrise and sunset, is 
also clearly perceptible with solar altitudes higher than those at which the 
white spot now appears and disappears, the phenomenon is at once removed 
from the category of optical to that of real change,—it may be temporary as 
referred to the luni-solar day, or of a more lasting nature if the surface 
itself should undergo a physical change. This will to a great extent pre- 
clude the expression of opinion, which is generally founded more or less on 
insufficient evidence ; observation alone can guide us to a safe conclusion 
in connexion with the questions raised on Linné. While refraining from 
expressing an opinion, we ought not to relax in collecting, arranging, and 
discussing evidence, as the only means by which we can obtain such an 
acquaintance with the phenomena of the moon’s surface as may enable us 
finally to dispose of such questions as are at present agitated respecting them. 
The change above alluded to is best elucidated by the following records of 
observation. 
The first notice of change occurs in the following extracts from Mr. Birt’s 
note-book :— 
«10.30. During the last half-hour a decided change has occurred in the 
appearance of Linné * * * The cone is no longer visible, nor the shadow, but 
a somewhat bright white spot, larger than I E’ 3 [the southern of the three 
craters to the N.W.], and nearly as large as I EH?!” [the middle of the three 
craters |. 
Lhave received from Mr. Gorton a drawing of Zinné made by Mr. Wil- 
liams of Liverpool, on the evening of June 26, at 11 p.m., in which Linné is 
represented as a white spot. This differs so very materially from the earlier 
observations that a correspondence ensued, of which the following is the 
result :— 
«‘ Although the drawings [Mr. Huggins’s, Mr. Carpenter’s, and Mr. Wil- 
liams’s] were made on the same evening, and differ amongst themselves, 
there does not appear to be any contradiction. Some observers saw the cone, 
another the opening, and others the bright white spot, the formation of which 
appears to have been actually witnessed. Mr. Joynson places the observa- 
tions of Mr. Birt and those of Mr. Williams in conjunction with his own in 
juxtaposition, thus :— 
1868. Mr. Birt reports. Messrs. Joynson & Williams report. 
June 25, 10.0 Cone-shadow well marked. A bright point. 
10.30 Cone disappeared; asome- Spot duller and flatter. 
what bright white spot. 
10.45 Spot as drawn [7. e. the ordi- 
to dinary white spot]. Moon 
11.80 low.” 
Mr. Joynson adds, “I think it is quite clear that the cone or bright point 
gradually took the aspect of a spot, and as it enlarged it became duller and 
flatter.” 
ee 
