SCIENTIFIC NOTES. 147 



and if a still larger number, they are printed from zinc. Mr. E. 

 Edwards, the inventor, has also several most interesting processes 

 which work with these. By one he can transfer any writing or 

 drawing done by common black ink to a stone, without the aid of 

 photography, and print off perfect copies by the ordinary litho- 

 printing process. This is used for catalogues, &c, and is, as Mr. 

 Edwards said to me, a dangerous process, for a man's signature 

 can be copied so that he could not tell it from the original himself. 

 By another, any drawing or writing is done upon a glass plate 

 coated with collodion, and this is used to print from. But the 

 stone process is the one with which they do the bulk of their work, 

 and it is so cheap that it can be used to illustrate ordinary business 

 price lists, &c. 



Of the sunlight, which does all this for us, we have no satis- 

 factory measures. Whether the sunlight is more this year than 

 it was last no man can say, but many want to know ; and 

 attempts have not been wanting to devise something which should 

 record the sun's power. I have only time to mention two of 

 them. The first : took a perfectly round and clear globe of glass, 

 about 4 inches in diameter, and placed it into a hemispherical cup 

 of wood that just fitted it, and exposed it to the sun for one 

 month, and then changed the wooden cup ; this was done for each 

 month in the year, and each wooden cup now contains an exact 

 record of the sun's power for that month, but unfortunately it is 

 written in such characters that no one can read them. When they 

 were shown to me I could not but join in the regret expressed, 

 that the results of the experiment could not be determined with 

 any degree of precision ; the sun-light concentrated by the glass 

 had burnt away a part of the wood proportioned to its intensity. 

 The other is the invention of Dr. Boscoe, of Owen's College, 

 Manchester, where he showed the whole apparatus to me and 

 asked me to make experiments in Sydney so as to combine them 

 with those in Europe, and I gladly agreed to do this. The test of 

 the sun's power in tins case is a piece of sensitive paper carefully 

 prepared, and having a known relation to the sensitiveness of all 

 other pieces used for the same purpose. The paper is in the form 

 of a long tape enclosed in a light tight box, with mechanism that 

 brings a fresh piece of paper under an open half-inch hole in the 

 top of the box whenever a signal is sent from the clock. 



Seven signals are sent at the beginning of each hour (or more 

 if desired), so that six separate parts of the paper are exposed to 

 the sun. The first is exposed 1 second, next 2 seconds ; 4, 8, 

 16, and 32 seconds respectively. These are compared afterwards 

 with a, coloured scale, and the effect at each interval recorded for 

 comparison with other years and places ; the intervals will be so 

 proportioned that the whole of the silver will be deposited ' in 

 something less than the maximum exposure. 



