362 Prof. G. G. Stokes, On the Arbitrary Constunts [June 3, 
before entering them. It seems probable that Struvite may be 
formed in ordinary soils through the agency of low forms of life; 
if this is a fact 1t may, to a certain extent at least, account for 
the “fixation of ammonia in the soil,” as the highly crystalline 
Struvite is a very insoluble compound. 
Perhaps I may be allowed here to suggest that if the soil in 
Fairy rings is carefully examined Struvite will most likely be 
found in it. 
I have also been led to think the formation of Calculi in the 
body may arise from the production in it of ammonia by micro- 
organisms. I have already stated that certain micro-organisms 
found in the human mouth produce these crystals with great facility. 
This fact has led Dr Cunningham and myself to suppose they may 
be the cause of the deposition of tartar on the teeth. Analyses 
of the saliva show the presence in it of considerable quantities of 
magnesium and calcium phosphates in solution. Ammonia is only 
wanted to cause the formation of ammonium-magnesium phos- 
phate, and to throw out of solution the calcium phosphate, and 
these salts are both constituents of Tartar, and we have shown 
that certain micro-organisms commonly found in the mouth -do 
produce that substance. We offer the suggestion that tartar may 
be produced in this way, but frankly acknowledge that further ex- 
periments must be made before we can declare that such is the case. 
Since the above was written I have found that if a little 
dilute solution of ammonia is introduced beneath the surface of 
the agar-agar in a tube, small but well-shaped crystals of Struvite 
are formed in a few minutes. 
(4) Mr W. GARDINER exhibited specimens of the leaf and in- 
florescence of Aciphylla squarrosa, presented to the Botanical 
Museum by Messrs Veitch. 
June 3, 1889. 
Mr J. W. Ciark, PRESIDENT, IN THE CHAIR. 
The following Communications were made: 
(1) Note on the Determination of Arbitrary Constants which 
appear as Multipliers of Semi-convergent Series. By Professor 
Sir G. G. STOKES. 
In three papers communicated at different times to the 
Society*, I have considered the application of divergent series to 
the actual and easy calculation, to an amply sufficient degree of 
accuracy, of certain functions which occur in physical investigations, 
* Camb. Phil. Trans. Vol. 1x., p. 166; Vol. x., p. 105; Vol. x1., p. 412. 
