These plates were placed in the frame on the ground, as has been previously explained. Known weights falling from known heights were made to strike the plates exactly in the centre. The weights consisted of bronze spheres, one weighing 3-1/2 oz. (100 grammes) and another of twice that weight. 1st. _Ordinary glass_ resisted the weight of 3-1/2 oz., falling from heights of 8 inches (0A.20 m.), 12 inches (0A.30 m.), 16 inches (0A.40 m.), but was broken by a fall of 20 inches (0A.50 m.). 2nd. _Toughened glass_ resisted the blow of the 3-1/2 oz. weight falling from heights of 20 inches (0A.50 m.), 40 inches (1 mA"tre), 60 inches (1A.50 m.), and 6 feet 6 inches (2 mA"tres). The 7 oz. weight (200 grammes) being substituted, the plate was broken by it, falling from a height of 60 inches (1A.50 m.). _Rectangular plates, 6 inches_ (0A.158 m.) _by 4-3/4 inches_ (0A.120 m.) _and 1/6 inch_ (0A.004 m.) _thick_. The same conditions were maintained as in the previous trial. 1st. _Ordinary glass._ The 3-1/2 oz. weight was allowed to fall from heights of 1 foot (0A.30), and 16 inches (0A.40 m). It was broken by the second blow. 2nd. _Toughened glass._ This resisted the 7 oz. weight falling from heights of 2 feet 4 inches (0A.70 m.), and 2 feet 8 inches (0A.80 m.), but broke when the weight fell from 39 inches (1 mA"tre). It appears then from these experiments, that toughened glass will resist a blow five times as great as ordinary glass, and will bear seven times as great a weight. I have now detailed most of the useful experiments which have been made by competent observers upon toughened glass, as well as some which have been conducted in my own laboratory. The result of my own personal investigations I will now lay before the reader. I was consulted some time ago by a gentleman interested in the introduction of toughened glass into this country, as to whether this kind would become untoughened in time. I feel no hesitation in stating that when the process has been perfectly done, the glass will remain in the same state for any length of time, provided it be not treated in any way which is calculated to rupture the external hard bond that holds together the inner particles of the glass. I feel quite sure, that no fear of this kind need interfere with the benefits, whatever they may be, which are to be derived from submitting glass articles to the toughening process.