‘Such is, in fact,’ he concluded, ‘the great condition to be satisfied in the application of lightning conductors, which is virtually nothing more than the perfecting a line or lines of small resistance in given directions, less than the resistance in any other lines in the building, which can be assigned in any other direction, and in which, by a law of nature, the electrical agency will move in preference to any others. The popular objections to lightning conductors on the ground that they invite lightning to the building, that we do not know the quantity of electricity in the clouds, and that hence they may cause destruction, are now quite untenable, and have only arisen out of a want of knowledge of the nature of electrical action. What should we think of a person objecting to the use of gutters and rain-pipes for a house, on the ground of their attracting or inviting a flow of water upon the building; and since we do not know the amount of rain in the clouds, it is possible that the building may be thereby inundated,--yet such is virtually the argument against lightning conductors.’
Mr. Snow Harris, as already mentioned, received the honour of knighthood in 1847; and after this date lived in comparative retirement for twenty years at his residence, Windsor Villas, Plymouth. However, he was called upon, in 1855, to undertake one more important work in designing a perfect system of lightning conductors for the new Houses of Parliament at Westminster. It was on the initiative of Sir Charles Barry, the architect, that the proposal was made by the Board of Works to Sir William Snow Harris, who accepted it with all his old eagerness for serving the cause of lightning protection. Accordingly, he drew up a plan, which he himself characterised, in a letter to the President of the Board of Works, dated February 14, 1855, as ‘somewhat costly,’ but which he felt sure would be absolutely certain ‘for insuring the safety of the buildings against one of the most terribly destructive elements of nature.’ In its essence, the plan consisted in protecting all the most elevated parts of the Houses of Parliament, including the towers, by ‘a capacious metallic conductor of copper tube, two inches in diameter, and not less than one-eighth of an inch in thickness,’ to be fastened together ‘by solid screw plugs and coupling pieces,’ and ‘secured to the masonry by efficient metallic staples.’ To do this, Sir William Snow Harris calculated, would involve an expenditure of somewhat over 2,000_l._, but nothing less would accomplish it. ‘What I have recommended,’ he wound up his letter, ‘has been the result of very serious and attentive deliberation, and I conscientiously think that what I have proposed is absolutely requisite to a permanent and satisfactory security of the buildings against the destructive agency of lightning.’ The Board of Works entirely adopted all the recommendations of Sir William Snow Harris, and, in accordance with them, there was included in the Civil Service Estimates laid before the House of Commons in the session of 1855 a vote of 2,314_l._, on account of ‘works necessary for securing the new Houses of Parliament against danger from lightning.’