THE ATTAINMENT OF VERY LOW TEMPERATURES 5 



coil can not be subjected to a back-pressure of over one atmosphere. 

 I have, however, found it to be mechanically impossible to wind 

 the spirals too closely. 



It is practically impossible to further increase the rate at which 

 the compressed gas loses its heat, but by means of an arrangement 

 which I shall next describe I have under certain circumstances suc- 



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a 



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Fig. I. — Eddies formed by 

 passage of gas through 

 orifice. 



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Fig. 2. — Regenerator coils. 



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B 



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ceeded in increasing the refrigerating efficiency of the expanded gas 

 as it passes over the outside of the coils. 



I have already referred to the fact that when a stream of gas passes 

 across the edge of a plate at right angles to its path, or enters or leaves 

 an orifice with square-cut edges, eddies are formed as in the figure i. 

 It occurred to me that by placing sheets of perforated vulcanized fibre 

 between the horizontal spirals, which make up the coil, such eddies 

 would be set up in the gas, and that the jets of gas passing through 

 the holes would themselves form eddies both by their mutual action, 

 and by impinging on the copper coils. Such an arrangement would 

 be much more effective in overcoming the tendency of the gas to flow 

 in streams, parted rather than broken up by the curved surface of the 

 pipes. Further, the fibre being a highly non-conducting material 

 would insulate the adjacent sections of the regenerator coil, and thereby 

 increase its efficiency. 



In the early part of the year 1904 I constructed two similar regen- 

 erator coils, each 20 cm. long and 7.2 cm. in diameter, wound about 

 a tube I cm. in diameter, surrounding the valve rod. One of the coils, 



