Full Details

Name and Model Number Hazen-Williams
Hydraulic Slide Rule
by Dennert & Pape
Country of Origin Made by Dennert & Pape in Germany for Ledder & Probst Co., Boston
Date of Manufacture c. 1905 - 1910
Front Scales Special hydraulic flow
Back Scales Special hydraulic flow
Scale Length 25 cm
Type of Rule Slide Rule
Construction Celluloid on mahogany. Screws at both ends of front scales to stabilize shrinkage of celluloid.
Area of Use Other
Comment For Hydraulic Engineering.
Hazen & Williams proposed their solution for pipe flow in 1903, and in 1905 they published Hydraulic Tables and
designed slide rule scales based on their equations. Note special scales on reverse of slide and flow constant tables on back.
Ledder & Probst sold engineering instruments in Boston from about 1905 to 1923, and they sold this example. They were agents for Dietzgen,
who listed this slide rule as model #1778A as early as 1910. An example with Dietzgen markings is at the MIT Museum, and one with the
Ledder & Probst markings is at the Harvard History of Science Museum. I conclude that this example was made c.1905 - 1910.

Rarity RRR
Donor Collection of Ed Chamberlain
Match Number 129
(Click Picture for Details)

In conjunction with our 'donors' we assign a rarity rating to each item, based on the system devised by Herman van Herwijnen
(1929 - 2004), renowned Dutch collector, author, and creator of Herman's Archive, a collection of 5,000 slide rule images on CD.
• RR = Rare - 1 of 25 collectors has one; it may take a year to find an example in the marketplace.
• RRR = Very Rare - only a few known to collectors; may be several years before it comes up for sale.
• RRRR = Extremely Rare - a museum piece; unlikely that an example will come up for sale.