125 
In conclusion, I would say that the form of air calorimeter 
I have given as No. 1 is very well adapted for teaching, as 
it enables students to construct for themselves instruments 
of sufficient exactitude to yield numbers very closely 
agreeing with standard numbers, while for calorimetric 
investigations, where freedom from all error is the first 
requisite, the differential calorimeter is very well adapted. 
The latter may also be made with india-rubber joints, but, 
as there is pressure, I prefer to have the joints hermetically 
sealed. In determining the heat of combination by these 
instruments the same relative method is used as for specific 
heats. It will be obvious that one great advantage in these 
instruments is the very small amount of substance required 
to give the necessary deflection. I have found in practise 
that from 0’5 to 2 grammes is quite sufficient, the amount, 
of course, varying with the size of the instrument. 
MICROSCOPICAL AND NATURAL HISTORY SECTION. 
March 11th, 1878. 
Charles Bailey, Esq., in the Chair. 
“ On Bryozoa,” by Arthur Wm. Waters, F.G.S. 
When we meet with the term zoophytes it does not now 
give an idea of scientific accuracy, but we do not often 
think how literal a signification it had when first employed. 
The zoophytes have included organisms in many widely 
separated groups, as the Anthozoa, the Hydrozoa, Bryozoa, 
Sponges, and even the calcareous Algae, and these were at 
one time held by some of the school of Pallas to be, as the 
