Hourly Date Sequence In R

I am trying to produce a sequence of dates at hourly intervals. As an example I tried the following:

> seq(as.Date("1912-02-24 23:00:00"), as.Date("1912-02-25 08:32:00"), by="hour")

which produces an error, yet it works fine for by= year, month, day.

The documentation for seq.POSIXt {base} states that it should work for hour, sec, min, etc, yet all of these produce an error.

> ?seq.POSIXt

Thanks in advance.