278 Dr. Herschel’s Observations to investigate 
Apparent View into the Openings , under luminous Bridges ana 
Shallows. 
Dec. 27, 1799. A luminous passage across a large opening 
has all the appearance of a bridge going over a hollow space ; 
and I have no doubt but that it is at a considerable distance 
from the opaque surface of the sun. 
Jan. 4, 1801. A ridge which separates two openings much 
past the centre, shews its thickness on the following side : it 
has a shallow, the preceding side of which I see going down to 
the opening ; and it appears to me, that there is a considerable 
distance between the lowest part of that shallow and the dark 
surface of the sun under it. Nor can I help believing that I see 
aslant under it, towards the preceding side ; though I find it 
difficult to account for such vision, on the principles of solar 
perspective. 
Jan. 6 , 1801. The same opening is now further advanced 
towards the limb of the sun. It appears again to me, that on 
the preceding side I see far under the shallow. I suspect the 
part towards P to be of a deeper dark colour than that towards 
F ; * but the difference, if there be any, is not marked enough to 
be decisive. 
Depth of the Openings , indicated by their Darkness. 
Jan. 15, 1801. n h io'. One of the openings, which is near 
the preceding limb of the sun, is remarkably black. The tint of 
openings may perhaps assist us to infer their depth ; which must 
be greater in a direction towards us, when the opening is near 
the circumference, than when it is near the centre, if the 
• See Plate XVIII. Fig. 1 and 2 . 
