Malcolm, N. (1964). Scientific materialism and the identity theory. Dialogue, III, 115-125
[Reprinting collections]  
Citing Place (1956) in context (citations start with an asterisk *):
* if electrical discharges and corresponding lightning flashes occurred in the same region of the sky, but not at the same time, there normally being a perceptible interval of time between a discharge and a flash, then Smart (I believe) would not wish to hold that there was anything more strict than a systematic correlation (perhaps causal) between electric discharges and Lightning. Fn. 4: Mr. U. T. Place, in his article "Is Consciousness a Brain Process", also defends the identity theory. An example he uses to illustrate the sense of identity in which, according to him, "consciousness" could turn out to be a brain process is this: "A cloud is a mass of water droplets or other particles in suspension". I believe that Place would not be ready to hold that this is a genuine identity, as contrasted with a systematic and/or causal correlation, if he did not assume that in the very same region of space occupied by a cloud there is, at the very same time, a mass of particles in suspension.