SCIENCE-GOSSIP. 



197 



SOME NEW PHYSICAL APPARATUS. 



By James Quick. 

 I.— EXPANSION OF SOLIDS. 



"PHE continually increasing work done during 

 the last two or three years in practical 

 physics, and the number of physical laboratories 

 constantly being equipped in our secondary schools 

 and technical institutes, have necessitated consider- 

 ably more attention being paid to the requirements 

 of this subject and to the methods followed by 



Fig. 1. — Apparatus for Testing Expansion of Solid: 



the various science masters in the country. As, 

 however, a different class of students is found 

 in schools to that in university and other 

 colleges, it is necessary to bring before them 

 specially devised apparatus, arranged in such 

 manner that although capable of accurate quanti- 

 tative results, it will not present any complicated 

 ideas. That is to say, there should be only one 

 difficulty — one fresh question confronting the 

 student at a time, and then his previous instruction 

 ought to have supplied all knowledge required, 

 except the particular object of the experiment. 

 This difficulty is very frequently met with by 

 teachers in the early part of the session, when 

 giving students experiments to perform in thermal 

 expansion of solids ; because some of the present 

 methods, such as those requiring the projection 

 upon the screen of the ends of the rods under con- 

 sideration, or the viewing of them through a tele- 

 scope, necessitate grasping the idea of magnifying 

 powers, and this is a difficulty to some students. 

 These methods also generally require much setting 

 up and a good deal of time, which, when one has 

 a full course of work to get through, is to be 

 regretted, and frequently leads to the experiment 

 being struck out altogether. Mr. F. C. Weedon's 

 design ( J ) completely overcomes these difficulties, 

 as it does not depend upon any knowledge of 

 optics, but simply upon reading direct, by means 

 of a pair of good micrometers, of the expansion of 

 the rod in question through a range of temperature, 



(1) Mr. F. C. Weedon, of Alleyn's School, Dulwich, has got 

 over the difficulty in his experiments upon the expansion of 

 solids, by the design of the present apparatus in use there, 

 which should be a really serviceable addition to a physical 

 laboratory. 



precautions being taken to prevent radiation and 

 consequent expansion or contraction of any sur- 

 rounding part of the apparatus. 



The only knowledge, therefore, assumed as 

 possessed by the student is the principle of the 

 vernier — ■ an elementary portion of mensuration 

 that is instilled, at the very outset of a practical 

 physics career. The construction 

 of the apparatus is seen from fig 1. 

 It consists of a long zinc trough, 

 in which, upon struts, is placed the 

 rod, one metre long, the coefficient 

 of which is to be measured. A 

 burner is supported underneath the 

 trough, running the whole length 

 of it, and provided with a double 

 set of holes and two inlet gas pipes, 

 so that the water contained in the 

 trough may be heated to boiling - point. The 

 ends of the trough have stuffing boxes, through 

 which pass short bits of glass rods, abutting on the 

 one side against the ends of the rod and on the 

 other against two delicate micrometer gauges which 

 are supported in two firm cast-brass clamps fixed to 

 solid teak blocks from the base. A metal screen at 

 each end, faced inside with asbestos, prevents heat 

 radiating to the micrometer gauges, thus eliminating 



Fig. 2.— Expansion of Solids, Specimen Curve. 



any error due to their expansion. The supports 

 for the trough, burner, etc., are placed in a cold- 

 water trough, provided with inlet and exit pipes, 

 and running the whole length of the base, which is 



