M. Orcel is Francois Orcel
Worldcat entry for the book by Francois Orcel:
http://www.worldcat.org/title/radiesthe ... ef_results
Note, the title is simply "Radiesthesie Agricole", not "Radiesthesie Agricole et Humaine", that's another book, also by Orcel.
The following text was taken from a
website (accessed 7.2.18), apparently the text is from:
Journal officiel de la République française. Lois et décrets
Éditeur : Journaux officiels (Paris)
Date d'édition : 1913-08-03
Les importations de tissus en Gambie, - Les renseignements suivants sont extraits d'un - rapport de M. Orcel, agent consulaire do France à Bathurst : La Gambie importe annuellement pour 3mil- lions 260,000 francs de tissus, chiffre qui a une tendance à augmenter tous les ans. Les principaux pays qui prennent part à ce trafic sont : l'Angleterre (81 p. 100), la France (14 p. 100) et l'Allemagne (3 p. 100).
Google translation:
Imports of Fabrics in The Gambia, - The following information is taken from a report by M. Orcel, Consular Agent of France at Bathurst: The Gambia imports annually for 3 million 260,000 francs of cloth, a figure which tends to increase every year. The main countries taking part in this trade are: England (81%), France (14%) and Germany (3%).
The passage in Mertens concerning Francois Orcel is also in the first edition of his book and also in the Dutch translation.
Ian