credited with the first physical molecular model around 1860. The surviving model of methane is from his Friday Evening Discourse on 7th April 1865 at the Royal Institution, where he used croquet balls to illustrate different chemical structures:

Thus we distinguish the chlorine atom as univalent, the atom of oxygen as bivalent, that of nitrogen as trivalent, and lastly the carbon atom as quadrivalent. - this I believe I can show you by a very simple contrivance. I will on this occasion, with your permission, select my illustration from that most delightful of games croquet.