426 Proceedings of the Royal Society 
acquaint us with the duties undertaken by the director, neither 
does he indicate the nature of the logarithmic formulae which 
needed the concurrence of four or five geometers for their estab- 
lishment. The actual business described by him begins with the 
doings of the second section, composed of “ sept on huit calcula- 
teurs, possedant l’analyse et ayant une grande pratique de la 
traduction des formules en nombres.” 
These calculated 1°, the ten thousand first logarithms to nine- 
teen decimals. 
In regard to this part of the work, M. Lefort supplies us, some- 
what indirectly however, with some very distinct information. 
He says (page 996) that Prony had borrowed a copy of Briggs’ 
Arithmetica Logarithmica , which he returned enriched with an 
u errata preceded by a note to the following effect; — 
“ This ‘ errata’ is composed 1° of that which is at the top of the 
Latin introduction (of Briggs); 2° of the faults found by the 
citizens Leteilier and G-uyetant, calculators in the Bureau du 
Cadastre, on collating Briggs’ table with the great tables of the 
Cadastre. These latter faults are marked by (a particular sign) 
the sign 
Lefort goes on to say that this collation brought out thirty-two 
new faults, of which, however, he finds that four belong to the 
Cadastre table, leaving twenty-eight only to Briggs. Farther on 
he tells us that all the corrections for numbers above 10,000 refer 
to figures within eleven decimal places, leaving the twelfth, 
thirteenth, and fourteenth places of Briggs unchecked. From 
this I understand, although it be not explicitly so stated, that 
within the ten thousand, even these figures in Briggs had been 
examined. 
Now, here I shall take the liberty of making an interjection of 
my own. 
In March, while comparing my fifteen-place table with Vlacq, 
I thought it desirable to examine also the last places of Briggs; 
so the final groups of four figures in the Arithmetica Logarithmica 
were read with the corresponding figures in the volume now on 
the table, up to 3000. The readers found the labour of recording 
the discrepancies so great that they had to content themselves 
with a pencil mark when the difference was only unit, and with 
