COLLECTORS, like everyone else, are always in search of their very own El Dorado, and for book collectors, that search is finally at an end. One of the most important scientific book collections for years, the library of the Earl of Macclesfield, is to be sold at Sotheby’s starting on Tuesday. Such is the size of the collection that it will be disposed of over four sales in the course of this year.

Sotheby’s is calling it “the greatest scientific library offered at auction in modern times”, a description that may well be justified, for not only will tens of thousands of books go under the hammer, but every one predates 1760.

“I have never before come across a library that was completed by 1760,” says David Goldthorpe, Sotheby’s leading book expert. “It is an excellent snapshot of the intellectual life of the period, to say nothing of the fact that it is full of relatively unknown books, which will therefore be totally fresh to the market.”

The library, which until now has resided at Shirburn Castle, Oxfordshire — Lord Macclesfield is moving to a smaller home and will not have room to house the books — is largely scientific in composition and the first part is devoted to natural history.

“It is an extraordinary collection,” says Dr Goldthorpe. “It includes many important books, including botany, which is strongly represented, as well as zoology. They are of great scientific interest, as well as being extremely beautiful.”

The books are, indeed, stunning, and range from exceptional examples of well-known works to equally exceptional examples of lesser-known tomes. Perhaps the most famous lot on offer is De Historia Stirpium Commentarii Insignes by Leonhard Fuchs, who gave his name to the fuchsia, dating from 1542. It is a first edition of a very famous herbal — books that listed the medicinal properties of plants and were used by doctors — and Mr Goldthorpe says it is the best copy that he has ever seen. It is estimated at up to £150,000.

Other treasures abound. Lot 54 is a book by Carl Linnaeus with a title too long to reproduce here: suffice it to say that it is the very inception of the scientific classification of plants and animals. Not only that, but the book, dating from 1735, possesses an extremely rare hand-coloured engraving by Georg Dionys Ehret, one of only four known in the world. The volume is estimated at £150,000 to £200,000.

And mention must be given to lot 13, a famous Florilegia. Written by Basilius Besler, and dating from 1613, it is the first pictorial record of flowers from a single garden. More than 1,000 flowers feature in its pages, amounting to 667 species, and some of the images in the book, such as the head of the giant sunflower, are widely familiar as they have been reproduced so frequently. The work is estimated at £150,000 to £200,000.

These are some of the most extraordinary items in the sale, but there are equally delightful works at much lower prices as well. Lot 76 is a book dating from 1715 called Ele-phantographia Curiosa, Seu Elephanti Descriptio, the first book devoted entirely to the elephant.

“Not only does it talk about their characteristics, but it tells you how to train them, domesticate them and hunt with them,” says Dr Goldthorpe. It has a sale estimate of £3,000 to £4,000. Equally, Lot 75 contains two works bound in one volume, one of which is An Essay on the Nature and Qualities of Tea, the first English work solely about tea. It is estimated at £1,500 to £2,000.

Bibliophiles everywhere will equate this sale to achieving nirvana. And if all that were not enough, there will be three more sales later in the year.

Sotheby’s: 020-7293 5000, www.sothebys.com; Bloomsbury Book Auctions: 020-7833 2636, www.bloomsbury-book-auct.com; Dominic Winter Book Auctions: 01793 611340, www.dominic-winter.co.uk.