Popular science monthly . terminals ofthe sensitiverelay. This bellwill ring instantlyw hen a lightstrikes the selenium cell, and willcontinue ringing as long as the cell isilhimiiialfd. li may l)e placed in asleeping apartment at a distance fromtile room to be protected, so that theburglar will be unaware ofthe fact his light hassent in .in . .\ deviceof this \\(aild be valu-able fur the |)rolection ofvaults. The seliiiiiiMi (ills may bepurchased Irom scientific su[)-ply houses at a cost of aboutii\e dollars each. The relayshould be as sensitive aspossible; a good pola
Popular science monthly . terminals ofthe sensitiverelay. This bellwill ring instantlyw hen a lightstrikes the selenium cell, and willcontinue ringing as long as the cell isilhimiiialfd. li may l)e placed in asleeping apartment at a distance fromtile room to be protected, so that theburglar will be unaware ofthe fact his light hassent in .in . .\ deviceof this \\(aild be valu-able fur the |)rolection ofvaults. The seliiiiiiMi (ills may bepurchased Irom scientific su[)-ply houses at a cost of aboutii\e dollars each. The relayshould be as sensitive aspossible; a good polarizedrelay may suftice but a galvanometerrelay is preferable. The battery should consist of asuliicieiit number of dry cells (these \-be (jf the small llashlight t\pe) to iiairlycause the closing of the relay contactswhen the selenium cell is in the dark, andwhen the k spring of the relay is iusulhcient tension to prevent slicking ofihe contacts after the light ;ucobstru( led. When the (ell i> Above: The dry cells connected in : The plan of the connections whenseveral pieces are to be set off simultaneously ^^ The selenium cell isthe eye of the crea-ture which whenilluminated con-tacts the relay ted the relay should close jiromptly,and when the light is removed the backspring should pull the contacts apartwithout hesitation. In general thelarger the number of batteries the moresensitive v\-ill the apparatus be, but withordinarv selenium cells the normalcurrent should not exceed a few thou-sandths of an ampere. If the currentis too large the temperature of the cellmay rise to thepoint at whichselenium beginsto melt; this willdestroy the use-fulness of the the relay,acting as thebrain, we may-lead connectionsto whatever ap-paratus we desireto be actuatedwhen the seleni-um cell is stimula-ted by light. When severalpieces of appa-ratus are to be setoff simultaneously, for example theapparatus before described, a connec-tion arrang
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectscience, bookyear1872
