CHAP. VI] THE HOT AND COLD DETECTOK. 55 



Now my plants (lie writes) would be injured if the heat fell below 50 

 or rose above 90, and I therefore wished to have some contrivance which 

 should inform me in my own study whether the temperature were remain- 

 ing or not within these limits. For this purpose a thermometer was made 

 for me into which two platinum wires were inserted, which came in contact 

 respectively with the mercury at those two points (fig. 5). By this con- 

 trivance, when the heat either fell below or rose above these two points, 

 the mercury and platinum were not in contact, and a voltaic current could 

 not be maintained. Telegraphic communications were laid down from 

 these two platinum wires to my dwelling-house, and a large pair of zinc 

 and copper plates were sunk into the ground for a battery. By attaching 

 the wires to a galvanometer we can always ask how the temperature is ; 

 and, by attaching an alarum, a gardener might be warned of any accident 

 at any time of the night. I must say, that had I the care of so valuable 

 a collection of plants as that of Kew, I should never be easy till I had 

 such an apparatus in my bed-room to tell me if any of my plants were 

 under unfavourable circumstances. 



This hot and cold detector was also modified and used under 

 other circumstances than telling the temperature of a hot-house. 

 Many years ago Mr. Smee's father had a cottage at Clapton, on the 

 hanks of the river Lea. The garden abounded with fruit, which the 

 hoys in the neighbourhood were only too glad to avail themselves 

 of generally choosing the time for their thefts when the family 

 were at dinner. Now one day my father attached fine thread to 

 the wires of the battery, in such a manner that as soon as the 

 boys were fairly in the garden they must insensibly move one of 

 these threads. Immediately down went the alarum in the house, 

 out ran my father, followed by his brothers and by his brother-in- 

 law. The boys, surprised in the very act of taking the fruit, were 

 soundly thrashed, and one of them having a squint was marched 

 off into the house by my father, and then and there had to submit 

 to the operation of having it cut. I am afraid that boy's ideas of 

 right and wrong must have been from henceforth rather confusing. 

 He had done wrong, for the effect of which he immediately 

 derived benefit, which he would not have derived had he done 

 what was right and had kept out of the garden. Let us hope, how- 

 ever, that he possessed a contented mind, and that he went not forth 

 again to steal fruit, in order to derive further benefits therefrom. 



The beginning of 1851 found Mr. Smee re-writing and bring- 

 ing out in an enlarged form a third edition of ' Electro-Metal- 

 lurgy.' This was followed in the month of March by a short 

 treatise from his pen on ' Process of Thought,' which contains a 

 lengthy description of the ^Relational and Differential Machines.* 



* Woodcuts and explanations of the relational and differential machines are 

 to be found in the ' Mind of Man,' pp. 94, 100. 



