Letter from [Alan Archibald Campbell] Swinton, to Dr. H. Boins, "Engineering" Responding toa previous letter, offering his suggestion that it might be worth trying to cause a stream of positive particles, i. e. Goldstein's Canal Rays, and a stream of negative particles, i. e, Cathode Rays, to impinge upon one another in the hope that X-Rays would be generated where they collided. Mentions that the only known way of exciting X-Rays is to cause the nagative cathode rays to fall on a solid body which has relatively positive electrification, with his idea being to do away with the solid body and employ positively charged particles instead. 30 March 1921