951 



this description, and to the representation of the lamp which accom- 

 panies the paper. It was made by Sir Humphry's own hands, and 

 given by him to Dr. Lee, now Lord Bishop of Manchester, whose 

 father was Assistant Secretary to the Royal Society at the time of 

 Davy's Presidency. The excessive simpUcity of the contrivance is 

 most remarkable ; but this is one of the greatest advantages which 

 attended the invention. As the author remarks in the paper just 

 quoted, " All that the miner requires to ensure security, are small 

 wire cages to surround his candle or lamp, which may be made for 

 a few pence, and of which various modifications may be adopted. 

 And the application of this discovery will not only preserve him 

 from the fire-damp, but enable him to apply it to use and to destroy 

 it at the same time that it gives him a useful light." A month after 

 the invention Sir Humphry informed the Society that his cylinder 

 lamps had been used in two of the most dangerous mines near New- 

 castle with perfect success. 



The following papers were then read :— 



1. "On the Structure of the Dental Tissues of Rodentia." By 

 John Tomes, Surgeon-Dentist to Middlesex Hospital. Commu- 

 nicated by William Bowman, Esq., F.R.S. 



The author in this paper relates the results obtained from an ex- 

 tensive series of investigations on upwards of sixty of the more 

 typical members of the order Rodentia. He finds, that not only are 

 the teeth of animals of this order distinguished by strongly marked 

 structural peculiarities (hitherto not recognised) from other mam- 

 malian teeth, but also that the teeth of the several larger groups 

 are distinguished from each other by modifications in what may be 

 called the rodential type of dental tissue. Mr. Tomes pointed out, 

 in a paper published in Part 2 for 1 849 of the Phil. Trans., that in 

 the teeth of marsupial animals the dentinal tabes are continued into 

 the enamel. In the present communication he shows that the struc- 

 tural peculiarities which characterise and are confined to the teeth 

 of rodents are also mainly resident in the enam.el. The earlier pages 

 of the paper are devoted to a description of those structural condi- 

 tions which are common to the teeth of the whole order. Amongst 

 these, the author finds that the extremities of the dentinal tubes, 

 which in the lov/er part of the tooth communicate with the pulp- 

 cavity, become in the extruded portion sealed up by the development 

 of a layer of non-tubular tissue which is formed at and near the 

 apex of the pulj3-cavity. This closure of the dentinal tubes is not 

 however confined to the teeth of Rodentia, but occurs in all teeth in 

 those parts exposed to wear. A similar condition is found to obtain 

 in the osseous tissue which forms the antlers of the Deer- tribe. If 

 a portion of an antler previous to its losing its periosteum be exa- 

 mined, ordinary Haversian systems are found : but if an antler which 

 has been shed be examined, each of the larger Haversian systems 

 will be found to be lined by a layer of transparent tissue destitute 

 both of lacunae and canaliculi. The author considers these condi- 

 tions to indicate the existence of a general law, viz. that dense 

 tubular tissues, when about to be exposed to w^ear or about to be 



