Understanding a visual description of a circuit (easy)?
C1 was first connected to the dry cell to charge till V volts. Then C1 is connected to C2. So C1 should be connected to the 'fixed' terminals of DPDT switch and others must be connected to the 'throwable' terminals.

The schematic of the circuit with switch thrown to initial condition (connected to dry cell) is shown below.



The capacitor C1 is charged to V volts. So total charge stored in capacitor C1 will be
$$Q = C_1\times V$$

When C1 is connected to C2, C1 and C2 are parallel and hence they will share the charge to make the voltage across them the same. So the voltage across C1 decrases and that across C2 increases. Let the final voltage be \$V_f\$ then by theorem conservation of charge,

$$C_1V = (C_1+C_2)V_f$$
$$V_f = \frac{C_1}{C_1+C_2}\times V$$

So \$V_f&lt; V\$.