86 PETER GUTHRIE TAIT 



Amagat. He also projected a series of investigations upon solutions of 

 varying concentration, so as to test the applicability of the formula Aj(B + s + /), 

 where s represents the percentage amount by weight of the solute. In 1893 

 he published results of a preliminary character on three solutions of the 

 substances Potassium Iodide, Potassium Ferrocyanide, Ammonium Sulphate, 

 Magnesium Sulphate and Barium Chloride, and found that the formula 

 applied fairly well. Five years later he published a preliminary note on the 

 compressibility of solutions of sugar based upon experiments which were 

 carried out by A. Shand (Nichol Foundationer). The results were not 

 very concordant ; but they indicated that the effect of sugar was, weight for 

 weight, barely one-third that of common salt in reducing the compressibility. 

 Mr Shand was planning a continuation of the experiments, when his early 

 death deprived the Edinburgh University of an experimenter of real ability 

 and resourcefulness. 



The new compression apparatus, familiarly known as the " Big Gun," 

 was not received till 1 879 ; and it was first set up in a small cellar on the 

 basement of the north side of the College. Here all the experiments dealing 

 with the testing of the " Challenger " thermometers were carried out. The 

 accommodation was very limited, and the light was poor ; but in a few years 

 the apparatus was transferred to a much larger basement cellar, in the north- 

 west corner ; and here all the later experiments on compression were made. 



This change was part of a general expansion of the Physical Laboratory 

 consequent on the removal of the Anatomical Department in 1880 to the 

 New Buildings which were to be wholly devoted to medical studies. Till 

 that date the Dissecting Rooms occupied the top story of the north side of 

 the College with the exception of the small room which had served for a 

 physical laboratory under the care of Tait's successive assistants, W. Robertson 

 Smith, D. H. Marshall, and P. R. Scott Lang. During my first year of the 

 assistantship (1879-80) the whole suite of four rooms became transformed 

 into the physical laboratory. There was ample accommodation, so far as 

 mere area of floor space was concerned ; and it was possible to arrange a 

 junior laboratory and rooms for special magnetic and optical work. On the 

 basement Tait secured the large cellar already mentioned, in which were installed 

 the compression apparatus, the dynamo, the gas engine for driving the dynamo 

 and for working up to high pressures, and latterly the " guillotine " for the 

 impact experiments to be afterwards described. In a neighbouring cellar 

 fifty secondary cells were in due course installed ; and there was also a third 



