He used two boxes each with a rubber diaphragm which shot out white smoke rings when the diaphragm was struck. Thomson wrote to Helmholtz on 22 January 1867:
Siya na ginamit ng dalawang kahon ang bawat isa ay may goma dayapragm na pakikipagsapalaran out puting usok rings kapag ang dayapragm ay Struck. Thomson wrote sa Helmholtz sa 22 Enero 1867: