Experimental Philosophy Lectures at London.
‘In this little Treatise I have endeavour’d to explain that Part of Mr. Newton’s Principia, which is Fundamental to the Rest of the Divine Book; and particularly to the System of the World. And I have all along taken Care to render Things so far plain and easie, that they may be understood by all those that will bestow some Application upon them, and have a competent Share of the necessary Furniture, namely Algebra and Conick Sections….’
Humphry Ditton, The general laws of nature and motion (London, 1705).
Ditton’s The general laws of nature and motion (London, 1705).
Worth’s copy of Humphry Ditton’s The general laws of nature and motion (London, 1705) and John Theophilus Desaguliers’ A system of experimental philosophy, prov’d by mechanicks (London, 1719) reflect the growth in Newtonianism in early eighteenth-century England. Both men were committed to spreading the ideas of Newton by explaining them in simple terms via experiments.
Ditton (1675-1715) was a non-conformist who owed his 1706 appointment as a mathematics teacher at Christ’s Hospital in London to Newton and his reliance on Newton shines clearly from his preface which repeatedly reminds the reader that the subject matter in the book is ‘so absolutely Mr Newton’s Property that I dare hardly pretend to call anything mine’. Where Ditton’s influence came into the play was not in the subject matter but in its interpretation and projected audience. Whereas Newton had written the Principia for skilled mathematicians, Ditton’s goal was ‘not to entertain those that are of an advanced Standing in this noble Philosophy, but to introduce those that wou’d be acquainted with it, and have as much Mathematicks as is necessary to qualifie them for it’. With this in mind he chose to write his work in English, rather than in Latin, arguing that there was ‘no Reason why a Multitude of very capable Minds shou’d be debarr’d from them merely for want of a Language’. Ditton’s potential audience was thus far wider than that contemplated by Newton. His book, for ‘the use of the Younger Mathematicians’, was designed to be sold as a textbook for the teaching of mathematics at school level but it could also serve as an introduction to Newtonianism for the rapidly growing experimental philosophical lecturing market at London and beyond.
As Stewart (1986) reminds us, Ditton’s appointment to Christ’s Hospital a year after writing this work encapsulates the two potential markets: Christ’s Hospital Mathematical School had originally been established in 1673 and was designed to provide mathematical and navigational training for boys interested in a naval career but its connection with the Marine Coffee house, a popular venue for public lectures on experimental philosophy, ensured that a textbook for the Christ’s Hospital might also appeal to the novice experimental philosophers who crowded the public lectures given by Ditton and his colleagues. The commercial milieu of Ditton’s work may be glimpsed in his decision to dedicate the book to Charles Du Bois, a treasurer of the East India Company who became a Fellow of the Royal Society in 1714.
Ditton’s collaboration with William Whiston, the former holder of the Lucasian chair at Cambridge, who had moved to London after his dismissal on religious grounds, demonstrates that the worlds of Newtonianism at the universities and in the City were not necessarily all that distinct. In London, Whiston simply re-printed his Cambridge lectures – this time in English to appeal to the wider market. Similarly, one of the most successful Newtonian public lectures at London had been trained in the University of Oxford before turning his attention to London: John Theophilus Desaguliers.
Desaguliers (1683-1744) came from a Huguenot émigré family, a fact which would stand him in good stead when he later sought to spread Newtonian ideas on the continent. He had gained his BA at Oxford in 1709 and from 1710 to 1712 had lectured there at Hart Hall while he studied for his MA. In 1712 he moved back to London and in the following years began his lucrative lecturing course on experimental philosophy, lectures which, as Fara (2004) points out, were heavily influenced by John Keill’s lectures at Oxford. Adept at attracting influential patrons he was made chaplain to James Brydges, who would later become the Duke of Chandos. This position added to his revenue, allowing him to concentrate on the matters which really occupied his attention: scientific rather than theological. Another influential patron was Newton himself and in 1714 Desaguliers was elected a Fellow of the Royal Society and later took over Francis Hauksbee the elder’s position there as curator of experiments. He became an active member of the Society, participating in the Newtonian debates at the Royal Society during this period.
Worth’s text by Desaguliers, the latter’s A system of experimental philosophy, prov’d by mechanicks (London, 1719) offers us a vital insight into the types of things Desaguliers lectured on during his successful experimental lecturing series. The publication itself was not initiated by Desaguliers but was rather an unofficial rendering of his London lectures at the Censorium by one of his former students, Paul Dawson. Dawson had been keen to publish the contents of Desaguliers’ lecture course not only because of his adherence to Newtonianism but also because publishing Newtonian textbooks was potentially very lucrative. In this instance Desaguliers reluctantly gave his imprimatur but a year later would see him involved in a contentious dispute with the same London bookseller, William Mears, over rival publications of a translation of Willem ‘s Gravesande’s Physices elementa mathematica experimentis confirmata (‘s Gravesande’s Newtonian lectures at the University of Leiden). As Wiggelsworth (2003) reminds us, ‘Experimental philosophy in eighteenth-century London was more than a means to demonstrate facts of nature; it was also about money’.
Dawson’s edition of Desaguliers’ System clearly falls into this category. At the same time it offers us a fascinating insight into the structure of Desaguliers’ London course in 1718. As the following listing of the contents demonstrates, what was on offer was very much experiment based, with an emphasis on utility. This was hardly surprising given the projected audience for experiments were much easier to teach than the abstract mathematics of the Principia:
The Definition of NATURAL PHILOSOPHY, and its first Principles.
MECHANICAL POWERS, and their Definitions.
How to make a heavy Body seem to rise it self.
Of the BALANCE.
Of the LEAVER.
Of the PULLEY.
Of the AXLE in the WHEEL.
Of the WEDGE.
Of the SCREW.
Of the LAWS of NATURE.
Definitions and Experiments.
A Description of the AIR-PUMP Mr. BOYLE made use of.
Experiments of the AIR-PUMP.
How to Condense the AIR, so that you may put what Quantity you please into a Vessel.
Of BAROMETERS, THERMOMETERS, and HYROMETERS.
Sir Isaac Newton’s COLOURS.
A Description of the Condensing ENGINE with its Apparatus.
A DESCRIPTION of ROWLEY’S HORARY, being a Machine to represent the Motion of the MOON, about the Earth, and the Earth, Venus and Mercury about the Sun.
Of these topics undoubtedly one of the most accessible of Desaguliers’ experiments was his experiment to prove Newton’s theory of colours as outlined in the latter’s Opticks. Indeed many of the experimental philosophy lecture courses concentrated on experiments connected with the Opticks, rather than attempting the lofty heights of the Principia. As the note on the experiment accompanying the above plate 10 demonstrates, these were experiments ideally suited to his audience:
Sir ISAAC Newton’s COLOURS.
Lights which differ in Colour, differ also in Degrees of Refrangibility.
‘If you apply any flat Side of a Prism to the Hole of a dark Room to receive the Rays which come from the Sun, these Rays which are different in Colour, will be separated by a different Refraction, and diverge from one another, (as in Fig. 1 Plate. 10) and appears distinctly in an oblong Figure on the opposite Wall: They will be refracted in this Order, viz. The red Rays will be refracted least, the Orange somewhat more, the Yellow more than that, the Green yet more, the Blue more than the Green, and the Purple most of all. Now to shew that these Colours were not made by Refraction, but were originally in the Rays of the Sun; if you refract any one of them never so much with a Prism, as for Example, the Purple in the first Figure, it will retain the same Colour.
If you contract these refracted Rays with a Burning-Glass, they will all converge to the Focus of parallel Rays, as in the second Figure; where if you receive them on Paper, they will appear White: And to shew farther, that White is a Composition of all these Colours, if you intercept the blue Ray with a Piece of Paper, between the Focus and the Glass, the White at the Focus will appear Reddish; if the Reddish be intercepted it will appear Blueish. So that if one of these Colours is wanting, the White is imperfect.
Fig. 3. If you receive all the Rays on a Piece of Paper, as at L, Figure 3d. between the Focus of parallel Rays and the Glass, they will appear with their proper Colours in their right Order, and converging towards one another; but if they be received beyond the Focus, they will appear in their proper Colours on the Paper, and to have diverged from one another, whence their Order will be inverted, viz. the purple Ray will be in the Place of the Red, and the Red of the Purple.
To shew that the Rays which differ in Colour, tho’ they have the same Incidence, are differently refracted, place a tall Piece of Wood with an Hole in it, Fig. 4, and a Prism behind that Hole at a convenient Distance from the Window; then with it refract the several Rays one after another from the Hole in the dark Room, to the Hole in the Piece of Wood, and each of the Rays will be differently refracted on the opposite Wall. Viz. The Reddish will be least refracted, and uppermost; the Orange next, underneath; the Yellow next, the Green next, the Blue next, and the Purple lowest of all.
Those Objects whose Parts are so disposed, as to reflect any one of these Rays more than the rest, and in a great measure to absorbe and stifle the others, appear to be of that Colour which they most reflect; whence a blue Ray when refracted on a blue Object, appears much stronger than when it is refracted on one of a different Colour, and so of the rest. If you look thro’ a Prism on an Object of any one Particular, V. G. Green, you will see it in all the other Colours; but the Green being the most powerful, the Object to the Sight of the naked Eye will appear altogether of that Colour.
Since White has been proved to consist of all Colours; it follows from hence, that those Objects which appear White to us, are such as are disposed very curiously to reflect all Colours, and the greater or less this Disposition is in the Superficies of the Object, it will appear accordingly of a quite White, or else of a somewhat shaded Dark-brown, or some other intermediate Colour; and those Objects which are very little, or not at all disposed to reflect these Rays, will appear Black.
It may be so contrived by darkening a Room, and by that means letting Beams of Light fall forcibly upon a black Object, that it shall then appear exactly White to the Eye.
If you expose two Pieces of Marble to the Sun, one White, the other Black, the Black will be hot, and retain the Heat longer; for as the White reflects, so the Black absorbs the Rays of the Sun.
If an oblong Piece of Paper placed before a Window, be viewed at such a Distance thro’ a Prism, that the Light from the Window on the Paper may make an Angle, equal to that which is made by it, i.e. the Light reflected from the Paper to the Eye, Provided the Paper be terminated with Sides parallel to the Prism, and the Horizon, and distinguished by a perpendicular transverse Line into two Halves, the one of an intensely blue Colour, the other intensely Red: If the refracted Angle of the Prism (i.e. its two Sides thro’ which the Light passes to the Eye) be turned upwards, so that the Paper may seem to be lifted upwards by the Refraction, its blue Half will be lifted higher by the Refraction, than its red Half; but if it be turned downwards, so that the Paper may seem to be carried lower by the Refraction, its blue Half will be carried something lower thereby than its red Half; because in both Cases the Light which comes from the blue Half of the Paper thro’ the Prism, to the Eye, is more refracted than that which comes from the red Half.’
Desaguliers, A system of experimental philosophy, prov’dby mechanicks (London, 1719), pp 187-191.
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