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Richard Helsham’s Lectures in Natural Philosophy at Dublin.
‘By this means has natural philosophy within the compass of one century been brought out of the greatest darkness and obscurity into the clearest light; and this has been chiefly owing to the unparalleled abilities, and indefatigable industry of that great and accurate philosopher Sir Isaac Newton…’
Helsham, A course of lectures (Dublin, 1739), p. 2.
Richard Helsham (c. 1682-1738), a native of Kilkenny, was educated at Trinity College, Dublin, where he took his BA in 1702 and was elected a fellow in 1704. By 1705 he had taken his MA and by 1713 was awarded an MD. At the opening of the School of Medicine at TCD in 1711 he was asked to give a lecture on natural philosophy and he continued this teaching in the ensuing years. In 1723 he was appointed Donegal lecturer in mathematics in 1723 and, in the following year, became the first holder of the college’s Erasmus Smith professorship of natural and experimental philosophy (1724-1738). During the latter part of his life he was appointed the regius professor of physic (1733-1738). Helsham was thus a central figure for the teaching of natural philosophy at the University of Dublin in the early eighteenth century.
While the Laudian statutes, with their focus on aristotelianism, officially still held sway at Dublin it is clear from other evidence that natural philosophical teaching there was beginning to move with the times. Certainly by 1703 a student was recounting reading Descartes, Gassendi and Locke, though it is clear that Newton was the preserve of the teaching staff. The period between 1683 and the early eighteenth century witnessed the foundation of the Dublin Philosophical Society, where eminent scientists such as William Molyneux met to discuss all things scientific. Links were fostered with the Royal Society and no doubt as a result St George Ashe (1658–1718), on his election as Provost of Trinity College Dublin in 1692, did his best to encourage the teaching of natural philosophy at the college. He would later leave his valuable collection of mathematical books to TCD. The Dublin Philosophical Society had been revived in 1707 by Helsham and Bryan Robinson following the difficult period of the late 1680s.
Robinson’s publication of the text of Helsham’s lecture course at Trinity, proved to be very popular and continued to be a compulsory text for TCD students until 1849, going through no less than eight editions in the process. The reason for this was obvious: it clearly explained the scientific discoveries of Newton. Helsham’s target audience was much the same as Whiston’s at Cambridge – their undergraduate cohort – and with this in mind Helsham carefully concentrated on explaining simple experiments (as the extract from his second lecture at the end of this webpage demonstrates). As Kelly et al (1999) explain, yet another factor in the publishing success of A Course was the simple certainty that pervaded the work: Helsham avoided contentious issues and deliberately concentrated on providing his readers with a coherent text which appeared to provide them with all the information necessary for their ultimate calling: to become clergymen of the Church of Ireland.
As the titlepage makes clear, this was a posthumous publication, undertaken by the Dublin physician Bryan Robinson (1680–1754) who had been one of Helsham’s students. The inclusion of this textbook in the Edward Worth Library, though obviously printed after Worth’s death in 1733, was undoubtedly due to Bryan Robinson, who, like Worth and Helsham, was a Trustee of Dr Steevens’ Hospital. Although the text itself is not solely devoted to Newtonian themes, the preface, by Robinson, firmly places it in a Newtonian context. At times Robinson uses direct quotations from the Principia and Opticks to outline Newton’s method. The subject matter of the initial lectures, attraction, is also solidly Newtonian based, with Helsham focusing on particles and force and investigating attraction and repulsion. From attraction he moves on to consider mechanics. This is followed by an investigation of hydrostatics. This was, as Kelly et al. (1999) remark, a topic which Helsham was particularly interested in given his work on the Dublin water supply. From hydrostatics the course moved on to a study of pneumatics and finished with an extended disquisition on light.
Lecture II. Of Attraction.
Having in my former Lecture proved from experiments, that there is a power in nature whereby the parts of matter, which are brought so near as to touch, do in some circumstances mutually attract each other. I shall now treat of such kinds of attraction as extend themselves to considerable distances beyond the point of contact, and on that account affect the mind more strongly, so as to convince it more fully of the reality of such a principle. Of this kind is, First, that attraction which obtains between glass and glass. Secondly, that of electricity. Thirdly, the attraction of magnetism. And lastly, that of gravity; of all which in their order…
Tho’ the principle of gravity, which comes next to be treated of, be diffused throughout the solar system, and may probably be extended so far as to reach the other systems of the universe; yet shall I consider it at present with respect only to the globe of the earth, which we inhabit; the parts whereof would by reason of the diurnal rotation be apt to fly asunder, were they not kept together by the influence of this principle; whereby likewise all bodies on or near the surface of the earth are made to tend towards its center. This power at equal distances from the center of the earth is always proportional to the quantity of matter in the body whereon it acts; for all bodies the light as well as heavy being let fall from the same height descend with equal swiftness, provided they meet with no resistance from the air, as will appear from the following experiment. Let a piece of gold and a feather be let fall from the top of an exhausted receiver at the same instant of time, and they will both arrive at the bottom at the same time very nearly.
The reason why the feather doth not reach the bottom quite so soon as the gold is that the receiver cannot be perfectly exhausted, and therefore the small portion of air which remains within, tho’ very much rarified, gives some small resistance to the descending bodies, which suitably to the nature of all resistance must retard the lighter body more than the heavier, and consequently cause some little difference in the times of the descent, which otherwise would be exactly equal. This being the case, it evidently follows, that the forces of gravity, whereby bodies descend, must at equal distances from the center be as the quantities of matter in the descending bodies; for it a certain force of gravity be requisite to carry down a certain quantity of matter with a certain swiftness, then is double the force necessary to carry down a double quantity of matter with the same swiftness; and triple the force to carry down a triple quantity, and so in proportion whatever to be the quantity of matter: so that the weights of bodies at equal distances from the center of the earth are always proportional to the quantities of matter which they contain; and therefore the quantity of matter in any body may be measured by its weight.
The gravity of a body at any place beneath the surface of the earth has been proved by Sir I. NEWT. to be directly as the distance from the center; that is supposing the earth’s radius to be four thousand miles a body which on the surface of the earth weighs a pound, will within the earth at the distance of two thousand miles from the center weigh only half a pound, at the distance of one thousand miles only a quarter, and so on till at the center it looses all its gravity.
It has been likewise proved that the force of gravity on the surface of the earth, and all distances beyond it, is in the reciprocal duplicate ratio of the distance from the center; that is, if a body weighs a pound at the surface of the earth, whose distance from the center is four thousand miles, it will at double that distance weigh only a quarter of a pound, and at triple the distance, only the ninth part of a pound, and so on, whatever be the distance the force of gravity will be reciprocally as the square of the distance. For is it not highly rational that the power of gravity whatever it be should exert it self more rigorously in a small sphere, and weaker in a greater, in proportion as it is contracted or expanded; and if so, seeing that the surfaces of spheres are as the squares of their radii, this power at several distances must be as the squares of those distances reciprocally. Tho’ strictly speaking, this be the law of gravity, yet where the distances from the surface are inconsiderable with respect to the earth’s radius, the force of gravity may be looked upon as equal at all those distances; thus for instance, the gravity of a body at the distance of half a mile from the earth may be looked upon as equal to the gravity thereof at the distance of a quarter of a mile; or at the very surface; because the difference is so small, that if it be rejected it will not occasion any error in calculations. And indeed on this supposition are founded most of the reasonings of GALLILÆO, TORRICELLIUS, HUYGENS, and other naturalists concerning the descent of heavy bodies; and by the help of the same supposition have the several theorems been formed relating to the acceleration of falling bodies, the spaces described, the times of the fall, and the velocities thereby acquired; as I shall now shew you.
If the force of gravity whereby a body descends remains unvaried, the motion of a body falling by such a force will be accelerated, and that uniformly; that is the velocity will increase, and the increments thereof in equal times will be equal. For let us suppose the time of the descent to be divided into a number of equal parts indefinitely small, in each of which by supposition, the force of gravity makes equal impressions on the body to carry it down; whatever velocity therefore the body receives from the impression of gravity in the first portion of time, it must receive as much in every other portion; since therefore setting aside all outward lets and obstacles the effect of every impression remains, the velocity given in the first portion of time, will be doubled in the second, tripled in the third, quadrupled in the fourth, and so on continually thro’ the several portions of time. So that the velocity of a body falling by the force of gravity will constantly increase in the same proportion with the time of the descent. Or in other words, the motion of a body carried down by the force of gravity will be uniformly accelerated; and the velocities acquired will be as the times of the descent from the beginning of the fall…
Hoppen, K. Theodore (ed.) (2008), Papers of the Dublin Philosophical Society (2 vols, Irish Manuscripts Commission).
Kirkpatrick, T. P. C. (1924), The History of Doctor Steevens’ Hospital, Dublin, 1720-1920 (Dublin).
O’Riordain, Turlough, ‘Helsham, Richard’, Dictionary of Irish Biography (Cambridge).
Weaire, Denis, Kelly, P; and Attis, D. A. (eds.) (1999), A Course of Lectures in Natural Philosophy [by the late Richard Helsham] (Dublin and Bristol).
Welch, H. T. (2004), ‘Helsham, Richard (1683–1738)’, Oxford Dictionary of National Biography, Oxford University Press.