PESE-LETTRES
letter scale
RENÉ GUÉRIN

the restored letter scale of Ren é Gu érin

With a lot of luck you will sometimes come across a really special letter scale on the internet and also from the shape of the letter scale you will immediately recognize the maker. Only the frame with the pointer part of this letter scale was offered on the website of a French antique shop. By the way, the dealer knew that it was design by René Guérin. René Guérin filed a patent application for 15 years on January 15, 1849. A patent was granted on March 9, 1849 and it was numbered FR7874. On March 21, 1849, a supplement was added to that patent. Some patent figures are further down this page. I found two other copies on the internet. In Belgium an incomplete copy can be seen on the website of Erfgoedinzicht, see here. In France a complete copy was sold on the website of Aquitania-Memoria, see this webpage. There is a short video of this copy on Youtube with introductory French texts, see there. The realized letter scale differs in details from the patent figures.

back of the letter scale

a quick determination of what weight sets the letter scale to zero grams, which turns out to be 19 grams. The weight of the letter plate to be made together with the suspension may not exceed 19 grams

the purchased scale part

animation: suspending the self-made letter plate sets the scale to zero [move the pointer over the photo]

In old technical textbooks from the years 1851, 1855, 1856, 1865, 1870 and 1885 a drawing of the Guérin letter scale is depicted, mirrored or otherwise. In the magazine Equilibrium 1990 no.3, on page 1374, the FR7874 patent is briefly discussed. Also the magazine Le Système Métrique of 1997, on page 1115, pays attention to this patent FR7874.
After two months of waiting, the purchased scale part was finally delivered to me by PostNL (on behalf of Mondial Relay and via Hermes). My plan became to make this very old letter scale complete again. First of all, the weight that causes the letter scale to reach zero is determined. That's 19 grams. After some calculations, the thickness and diameter for the brass letter plate and the diameter and length for the brass suspension bracket were determined. I also roughly determined the dimensions for the suspension hook. It is still possible to add some extra weight at the bottom of the letter tray for fine tuning. A wooden box with an adapted (sliding) lid was also planned. A storage box is partly visible on the patent drawings. The purchased new box with sliding lid was a bit too big, I reduced the height and width by sawing. The parts are then rejoined with wood glue. An extra plank with a recess cut to size is glued to the lid. The scale foot should be slid into this recess when setting up the letter scale. It fits just right. The scale frame with the rotatably attached pointer, the detached suspension bracket and the separate letter plate fit in the box, see photos below. The box has been treated with dark oak wood stain a few times.
The scale of my copy is made of glued-on paper. The scale values in grams indicate the French letter rate. The first printed weight limit of 7½ grams and 20 centimes has been crossed out. As of January 1, 1862, that first letter post weight limit was raised to 10 grams and 20 centimes. The letter post weight limit of 15 grams was also replaced by 20 grams. That weight limit does not fit on this letter scale. The paper scale shows 40 centimes at 15 grams. Above it is an arrow pointing up and the value 80 centimes. This is barely readable due to the leaked glue. That was the rate from 15 grams to 100 grams in the period July 1, 1854 to January 1, 1862. This copy was therefore probably purchased somewhere in that period and the measurement scale was adjusted to the new postal rate after 1 January 1862. That postal rate remained valid until January 1, 1871.
The measurement scale of the specimen in France is painted and has the values: 0, 7½ and 15, without a gram indication, and still readable between 7½ and 15 the rate of 40 centimes. That was the letter rate from January 1, 1849 to January 1, 1850 and again from July 1, 1854 to January 1, 1862. That copy is from 1849 or from the period 1854-1862.
The measurement scale of the scale in Belgium only shows the values: 0, 10 and 20, without a gram indication and without postage. This copy is from after January 1, 1862. This measurement scale is also painted.
The two copies on the internet have a letter tray in which reinforcement circles and also texts are pressed, it looks like embossing.

The text outside the inner circle on the letter plate in France: * EMPLOYÉ PAR L'ADMINISTRATION CIE DES POSTES * FABQUE 66. R. DES MARAIS ST MARTIN A PARIS The text inside the inner circle: PESE LETTRES GUÉRIN BREVET DE 15 ANNÉES and with much smaller letters: SANS GARANTIE DU GOUVERNEMENT	The text outside the inner circle on the letter plate in Belgium: * EMPLOYÉ PAR L'ADMINISTRATION CIE DES POSTES * EXPEDITION & EXPORTATION The text inside the inner circle: PESE LETTRES GUÉRIN BREVET DE 15 ANNÉES and with much smaller letters: SANS GARANTIE DU GOUVERNEMENT
the letter plate of the letter scale in France [source and can be found at Aquitania-Memoria]	the letter plate of the letter scale in Belgium [source and can be found at Erfgoedinzicht.be]

the two letter plates printed on paper

on the left the letter plate seen in Belgium, on the right the letter plate seen in France

the two letter plates printed on paper

the paper French letter plate placed on my brass letter plate

merely my homemade brass letter plate

the paper Belgian letter plate placed on my brass letter plate

the scale has stops at the beginning and end of the scale

the top stop is clearly visible on the left

the letter scale mounted on top of the storage box is ready for weighing

figure from the book Cours Elementaire de Mechanique from 1851 N.B. the scale foot is in the wood surface

figure from patent application FR7874 of January 13, 1849 N.B. here the letter scale is screwed to the wood

figure from patent FR7874 of March 9, 1849 N.B. the tilted rectangle is the inside measurement of the box below this is a cross-section of the box

as depicted in the Physics book for children: Slinger en Magneet in dienst van den Mensch from 1865

image with the scale foot on top of the wooden base plate

image from a physics book from 1885 with the scale foot screwed to the wooden base plate

image from an 1855 mechanics book with the title: allereerste gronden der practische en theoretische mechanica this image is similar to the one from 1851

the top plank on the sliding lid is quite thick	the sliding cover rests in the grooves	the thickness of the top plank on the sliding lid is clearly visible
the glued-on paper measuring scale only has stripes at 0, 7½, 10, and 15 grams	the crossed out value of 7½ grams and the added value at 10 grams	the pointer with the counterweight on the arm is exactly at zero grams here

the Guérin letter scale is in this box	sliding the lid open requires the use of both hands make use of the recess	the lid can be slid off completely this is not really necessary for mounting the scale base
the three scale parts are stored in it	the letter plate was removed first the suspension bracket follows	the scale frame with the rotatably attached pointer fits nicely in the box
now slide the scale foot into the recess on the lid	the scale foot is now mounted in the lid	then the lid can be closed again

then slide the suspension bracket into the tunnel at the bottom of the letter plate

the letter plate is thus connected to the suspension bracket

hanging this on the scale part requires precision because it is a very small suspension shaft and a small slot

the scale rotation axis and the very small suspension shaft	connecting the suspension bracket to the small suspension shaft	the suspension bracket now hangs properly on the axle
the Guérin letter scale is ready for use and is at rest at zero	here the Guérin letter scale is loaded with 10 grams	here a load of 15 grams is on the Guérin letter scale

the Guérin letter scale on the self-made box with sliding lid

the Guérin letter scale mounted on an also self-made hardwood box with overlay lid