My Special Item  Mein Besonderes Stück
Vlacq Table of Logarithms, 1742
Acquired during april 2004 at the Dutch Circle stand in a collectors fair from a retired instrumentmaker at the Agricultural University of Wageningen.
Shown to the audience of IM2004 on 26 September 2004, according to the following
Principles of Collecting:
"with the acquisition of a special item, a collector acquires at the same time the responsibilities of its stewardship, to preserve the item well until a proper destination has been found for its future, to assemble and keep knowledge about the object, and to share this with the public"
Numerous Years of Publication for Vlacq’s Log Tables
(limited scan from Leiden Museums, Bierens de Haan and ZVAB/antiquarian bookhandlers)
1628 FL (Arithm. Log. II) 
1636 D (10 x 100,000) 
1651 FL (100,000) 
1657 D (100,000) 
1658 D (7 x 10,000, octavo) 
1661 DFGL (10,000) 
1665 DFGL (100,000) 
1666 F (100,000) 
1670 F (10,000 postuum) 
1673 G (10,000) 
1681 L (10,000) 
1683 D (10,000) 
1689 G (10,000) 
1690 F (10,000) 
1695 G (10,000) 
1706 G (10,000) 
1721 Chinese Arithm. Log. II 
1721 G (10,000) 
1725 G (10,000) 
1732 G (10,000) 
1738 G (10,000) 
1742 L (10,000) 
1748 G (10,000) 
1757 GL (10,000) 
1760 F (10,000) 
1763 G (10,000) 
1768 G (10,000) 
1775 G (10,000) 
1778 G (10,000) 
1784 L (10,000) 
1790 L (10,000) 
1808 G (10,000) 
1821 G (10,000) 

LEGEND 
D=Dutch: "Nieuwe Konstige Tafelen … " 
F=French: "Tables de Sinus … " 
G=German: "Tabellen der Sinuum … " 
L=Latin: "Tabulae Sinuum … " 
Cooperation between Vlacq and de Decker
Adriaan Vlacq 
Ezechiel de Decker 


1600 born in Gouda 


1603 born in Leiden 

1621 moves to Gouda as surveyor & teacher 
1624 reads Briggs’ "Arithm. Log." and starts planning a completer version 

1625, 24/12: obtains copyright for plan 

1625, 17/12: signs partnership contract with D. 


1626, 4/9 publishes "Nieuwe telkonst part I" 
1626, 31/12: summons D. to calculate part II 
and appitiser for part II with existing logtables 

1627 publishes "Nieuwe telkonst part II" 

"Het Groote Werk": 10 x 100,000 
1628 publishes French and Latin versions of 
(Rediscovered by Haaften in 1920) 
"Arithm. Log. Part II extended" 

(Copper plates for tables used from D.) 


1631 moves to Rotterdam, maritime work 
1632 opens bookshop in London 

1636 prints first "own" version of 1628 Tables 

1642 opens bookshop in Paris 


1647 dies in Rotterdam 
1648 opens bookshop in The Hague 

1667 dies in The Hague 

Some other thoughts and questions on log tables
 Hundreds of errors have been reported in the Vlacq tables, presumably in the last digit(s), but largely corrected in newer editions
 Ranges (1100,000) are better expressed in digit precision (e.g. 4 digits in, by 7 out), which should be "balanced" to each other (Briggs was too precise with 14 digits out)
 Were John Napier’s logtables really practical?
With logarithms of sines, the calculation types are very limited:
only sin(a) : sin(b) = sin(c) : sin(x), as used in spherical trigonometry  Who calculated Vlacq’s Trig tables? Or was it copied from Edmund Gunter’s "Canon Triangularum"? Did Gunter compute these himself?
 Gunter introduced a logsine with values between 0 and 9.xxxxxxx, based on his assumption of an extremely large angle radius.
Why did logsin tables keep this caracter convention deep into the 20^{th} century, long after the sine had been redefined to a radius of unity, resulting actually in a negative logsine value?
Autor: Otto van Poelje