58 Mr Low on the Currents of Tide of the Pentiand Frith , Sfc. 
that country in the year 1774, the MS. having recently come 
into my possession. For the accuracy of the observations it 
cannot be expected that I should be in the smallest degree ac- 
countable : but every reasonable confidence on this point may 
be reposed in a naturalist to whose labours the late Mr Pennant 
was highly indebted; and whose merits Dr Leach has just- 
ly appreciated, when he has stated, that “ they were those of a 
laborious and accurate observer of nature, but which were 
scarcely known beyond the narrow circle of his particular 
friends 
“ In passing the Pightland Frith *f*, one cannot fail observing a 
number of currents, which appear like pretty large rivers run- 
ning in the midst of dead water, and can be seen at some dis- 
tance, owing to the many sounds of Orkney through which these 
currents proceed, and the many points and islands which break 
the main stream, and. give fresh motion to so many new cur- 
rents, which, by this new-acquired rapidity, forcing themselves 
a passage through the more equal course of the main tide, cause 
these irregularities so much wondered at. For example, the 
tide of flood setting from the N. W. meets with no resistance 
from any thing, except a few headlands in Orkney, and on the 
Caithness shore, till it comes to Cantick Head in Waes. There 
it meets a tide coming through Hoy Sound, which is broke into 
many streams by the Islands of Cava, Fara, Flota, Switha, and 
Swona, and kept in by the large island of S. Ronaldsha. The 
courses of all these lesser streams are quite across the great stream 
of Pightland Firth, but their rapidity is greater ; therefore every 
one will occasion an alteration in the great tide ; and this meet- 
ing of two contrary tides, when the water is much disturbed by 
it, we call a roust , which is often dangerous for boats, especially 
when the violence of the wind contributes to put the waves of 
that spot in a still greater rage. Again, the tide of Pightland 
Firth continues, in some measure, undisturbed, till it comes to 
Stroma, upon the north point of which, it breaks with prodigious 
violence, and goes off with vast rapidity, forming an amazing 
current, called the Swelchee ; as, on the south end, the tide, by 
* See Dr Leach’s advertisement to Mr Low’s posthumous publication, entitled 
the 46 Fauna Orcadensis.” 
■f Pightland Frith is the name sometimes given to the Pentiand Frith. 
