Florian Cajori
History of the Logarithmic Slide Rule
This book was originally published in 1909. The author was born in Switzerland but spent all his adult life as an academic in the United States. His book describes the history of the slide rule from its invention in the 1620s up to the start of the 20th century. Those of us living in the age of email, the internet and air travel can only marvel at the effort he must have expended in locating documents held in libraries all over Europe and extracting pertinent information.
This version was based on a copy in the Whipple Museum of the History of Science, Cambridge University.
The book also has 17 plates of slide rules.
The whole book can be downloaded in Word document format or as an Adobe PDF file.
| Chapter | Contents |
| Preface | The author deplores the absence of a book on the history of slide rules in view of their importance in many technical and scientific fields. |
| The invention of Logarithms and of the Logarithmic Line of Numbers | A short chapter on Napier's invention of logarithms and on Gunter's scale, which first represented logarithms in other than tabular form. |
| Gunter's Scale and the Slide Rule Often Confounded | Another short chapter clarifying the difference between Gunter's scale and a slide rule. |
| Conflicting Statements On the invention of the Slide Rule | Discussion of alternative statements on the invention of slide rules. |
| Disentanglement of the Main Facts | A crucial chapter where he cites numerous works published in the first half of the 17th century. Unfortunately at the time of writing he had not seen one of the key texts and his initial conclusion was corrected in an addendum to the book. |
| Development During the Second Half of the Seventeenth Century | A discussion on early slide rules, both linear and circular. It includes a description of the use of slide rules by Sir Isaac Newton for solving quadratic equations. |
| Development in England During the Eighteenth Century | During this period the two main lines of development were as tool for estimating the content of barrels (gauging) to determine the duty to be paid, by Everard, and as a means of estimating the volume of timber, by Coggeshall. |
| Development in Germany During the Eighteenth Century | Whilst there is evidence that slide rules were known in Germany at this time, there is little evidence that their use was common. |
| Development in France During the Eighteenth Century | A similar situation obtained in France to that in Germany - that is, there was an awareness of slide rules but little evidence of their use. The introduction of the metric system following the French Revolution could however be considered as a step which would make it easier to use slide rules for many common calculations. |
| Development in England During the Nineteenth Century (First Half) | Whilst there is evidence of many inventions the only real step of significance was the development of log-log scales by Roget. |
| Development in Germany and Austria During the Nineteenth Century (First Half). | There appears to be little progress relative to the 18th century. |
| Development in France During the Nineteenth Century (First Half). | The slide rule became widely used in France during this period, using both rules made in France and imported from England. The government even introduced a requirement for public servants to be able to use a slide rule. |
| Development in the United States During the Nineteenth Century | Cajori suggested that slide rules were little used in the US until the final decades of the 19th century. [I do however have a book published in New York which appears to contradict this.] |
| Development During Recent Times | This was the era when all the conceptual components of modern slide rules were introduced [there were of course advance in materials and construction techniques in the 20th century], including the cursor which was developed by Mannheim in France and whose scale layout became a production standard. |
| Slide Rules Designed and Used Since 1800. | Brief details of more than 250 slide rules. |
| Bibliography of the Slide Rule | Reference to around 200 published works. |
| Addenda | This addenda is critical as it is here that Cajori attributes the invention of the slide rule to Oughtred. A view that is now generally accepted. |