REVIEWS AND EXCHANGES 
173 
be very much exaggerated for clearness sake, I cannot tell how 
much, but probably 250 times. The near cold layer of air 
I have, at a venture, put as about three miles wide. I think it 
may have been ten or fifteen feet thick. 
The popular reasoning of the matter is : take a cup of 
water, look down into it, the bottom appears above its real level. 
You are looking from a thin medium, air, into a denser medium, 
water. The bottom of the cup is raised a quarter the depth of 
the water. The reverse holds good when a diver looks from 
water into air, he sees objects depressed. 
I hope I have made the whole explanation clear. It seems 
to me satisfactory, and I trust it may appear so to others, or, if 
not, that some one will clear up the complex problem. When 
I was looking at the Needles, dark thunderclouds were seen 
beyond the Isle of Wight, but for clearness sake I have not 
represented them in the sketches. A storm was probably raging 
in the Channel at the time : this would cool the air, and the cold 
heavy air would spread itself over the surface of the sea, creeping 
round the Island in the way I have suggested. I may add that 
had this cold air extended up to the Needles a different set of 
phenomena would have been witnessed, as the base of those 
rocks would have been raised. 
I remember now that on many different occasions I have said 
to myself that I could not understand the look of the Needles, 
and I have frequently heard the lady who was sketching and 
others make the same remark. 
I now more clearly recognise that variations in the air strata 
account for the apparent increase or decrease of the rocks : it 
often seemed to me that there was some other reason than the 
fall and rise of the tide only. 
Giles A. Daubeny. 
July 26, 1900. 
REVIEWS AND EXCHANGES. 
Ha}idhook of British Ruin. By Rev. W. Moyle Rogers, F.L.S. Duckworth & Co. 
Piice 5s. netl. 
There can be few better trainings for the observing faculties than “ critical ” 
botany. For this reason, in spite of not a little difficulty in its u^e — a difficulty 
which it would, we think, be mischievous to minimise — we have long recom- 
mended Babington’s Manual even for tyros. We should, perhaps, hardly suggest 
the study of brambles to an absolute beginner in botany ; but, independently of 
any view’s that may yet be tenable as to the fixity or non-fixiiy of some of the 
“ forms,” there can be no dispute as to the value of batology, which is, it may be 
well to explain, the study of frrambles, as a botanical education. Just as, before 
the publication of the first edition of Babington’s Manual in 1843, British botany 
in general had drifted away from the advance of the science on the Continent, so 
until the issue of The British Rubi by the same master-hand in 1869, the critical 
